What is the purpose of the purlins?

Thanks Renovator for your reply.

Forgive me as my answer may be ill informed. However, I was under the impression the strapping (purlins) were designed to allow ventilation/air space before the R 42 bats. Another framer on our job who has just finished up the siding provided the rationale that I have given you, but I may have misunderstood him. He definitely thought the omission was a big error and not to code for our area. There could have been additional venting spec'd in addition to ridge vent listed in original post that I have missed and would not be doable without those purlins. I would post the detail page from the architect but it is too large for GW.

Carol

I wanted to add that the term purlins was what the siding carpenter called them. The architect's notes/picture show these items in the following order:

shingles, building paper, plywood sheathing and 1"X3" strapping @24" O.C.The strapping is shown underneath the sheathing before the 2 X 12 roof joists (looks like LVL to me).

The architect goes on to show an air space and the R-42 bat insulation with the roof joist and 1"X2" strapping underneath the insulation and roof joist to anchor drywall to.

Carol

All I can think of is that the purlins take the place of rafter bay baffles to keep the insulation from touching the bottom of the sheathing and add a small amount of additional space for insulation. Perhaps they also allow discontinuous eave and/or ridge vents.

I'm not sure why this would be a code issue or why it couldn't be fixed. There is no substitute for details when problem solving.

Thanks, Renovator, your notes sound encouraging that it can be fixed with out ripping up the dormer roof.

The siding carpenter talked about vents so maybe he was referring to eave vents, but I can't see them in the plans (I will look again). We have lots of detail pages, sections etc on our plans, but all the subs need constant reminders to read all parts of the plan carefully and to follow it exactly. The subs tend to want to just look at the floor plans and ignore the detail pages, which I imagine is not uncommon. We did not specifically point it out to the framers before it was too late. However, they were contracted to follow the plan exactly as spec'd by the architect.

Carol

I'm going to guess that the purlins allowed ventilation air to travel around the dormer, etc That might also be accomplished with holes drilled through the tops of the rafters especially since they are so deep. You might need to use deeper ceiling strapping to maintain r42 but double styrofoam vent baffles might be enough.

The purpose of the ventilation is to allow moisture to escape from the rafter cavity. The source of moisture is likely to be a roofing leak so careful attention to flashing and valleys is very important above a cathedral ceiling. If the roofing is not yet installed, cover the sheathing with Grace Ice &Water Shield instead of building paper. With all the valleys that should not be a big up charge and cheap insurance.

Why is your architect not all over this?

This post was edited by Renovator8 on Sun, Aug 18, 13 at 8:31

Thank you Renovator for your guidance. I will explore the ideas of drilling holes for ventilation. The rafters are built from thick LVL lumber. I did not realize you could drill holes in that material. We will also investigate if we can use thicker ceiling strapping to accomplish the same as the purlins. I am glad to have these two leads.

We do have ice and water at all valleys and changes in roof pitch, and the siding guy who is also doing the flashing has so far done terrific work for us. We do have two Sun Tunnels running through that roof as well, so that is one more source of leak to watch out for. Lots to think about.

We do have lots of snow and cold, and I undetstand that makes roof ventilation even more vital if I am not mistaken (compared to a dry/warm climate anyway).

How do you usually insulate a cathedral ceiling? Do you speck for foam instead of the bats or rigid insulation. Are either of these materials something to explore given the missing purlins,.

Thanks again!

Carol

Purlins would have made sense to me if they were doing vent over roof design or to provide a bit more depth to get the insulation values up.

Nothing that can't be fixed with some rigid foam and a vent space Carol.

What does code call for up there in your attic/roof layer?

Here is a good article for you to read: http://www.finehomebuilding.com/how-to/articles/a-crash-course-in-roof-venting.aspx

Here is a link that might be useful: Crash Course in Roof Venting

Renovator,

You asked why the architect was not all over this. We were unable to reach him Friday, but will try again this week. I am not sure how much ice and water was used over the dormer roof (it has been shingled). We asked them to use it generously and I don't have a photo to show how much was covered.

Washington,

Good to hear from you on this forum. Glad to hear you think it can be fixed without substantial demo too. I appreciate the link -- lots of good information there.

I can't see anywhere on our plan that the architect spec'd for baffles between the rafters, but he must have intended for us to use them.

As per insulating in between the rafters (after the air space) I would rather use rigid insulation or the batts spec'd by the architect instead of foam, I have read that closed cell foam can lead to headaches. We are all (family of 6) living in the home. I would assume we would have to leave for a while after foam was applied and go to a hotel? I am very prone to headaches as it is.

As per code around here, I don't know what the requirements are for cathedral ceilings. The building inspector is coming Tuesday. It was the siding carpenter who told me their was a code problem. Hopefully after talking to the architect (assuming he is not on vacation) and the inspector we will have a clearer idea of our options.

Carol

Here is what I was thinking after a day of researching. Can we put furrow strips cross ways from rafter to rafter to guard the 1 inch air space, and then put 4 or so sheets of rigid insulation between each pair of rafters? I guess we would need baffles to vent at eaves as well?

The architect had pots lights in his attic design and we went with four insulated pot lights and these four boxes have been roughed in. Is this also a mistake as that will knock off the R value around each pot light. Is there another way to light this space? Can we use those stair washers or something in the short knee walls. There is just not roof for a flush mount. Any other lighting ideas for this space which is more energy efficient than these pots?

Carol

Carol
I can see no reason why the strapping is a code issue. I assume it was to be installed across the rafters, in which case does not allow eave/ridge venting anyway. If anything, I think its a good thing they did not strap it.

I see several issues with your design.
First off, r42 batts is low for your climate. IECC calls for r49 min. You also have no air sealing in your rafter space if installed as planned. The can lights in a space like that, in your climate, is a bad idea. There is low profile surface lighting options that can be had that you would use a simple 4" round box instead.
Also as mentioned, you really do not have a good means of venting right now. Assuming your eaves are vented soffits, here is my recommendation to solve all of your issues above:
have them install ripped strips of wood ripped to 1"x2" or so and nail them on each side of each joist, touching the roof deck. Take 2" of XPS foam, rip in strips the width between your rafters. Run a thick bead of caulk down the strips nailed (in the joint between the furring and the joist) and install the foam into the caulk, making it a snug fit. This gives you a sealed vent space from eave to ridge. This also gives you an r10. In your remaining 8 1/4" space, net and blow insulation rather than use batts. You can use batts, but I would go with blown product instead. A blown fiberglass can give you a slightly higher r per inch. The assembly gives you about an r43-44ish and a 1" vent. However I would recommend strapping on the bottom of the joists with 2x to gain another 1.5" bumping your assembly r to r49 to r50, which is just hitting code min.

Izerarc,

I am so glad to see your post. I am going to read and re-read tomorrow, and I will probably have a few more questions later (hope you will check back). For now I wanted to say thanks! I also wanted to clarify a few things and ask some questions right away.

The furrowing strips were to be installed between the rafters and roof sheathing to give a bit more depth to the rafters I assumed for insulation and air space. This strapping was not to be installed across the rafters, but to run the length of the rafters and under the rafters if that makes sense. Now there was to be a second set of strapping across the rafters to install the drywall to.

I agree the can lights are a bad idea -- don't know why they were spec'd by the architect so we will have to get rid of them and use different lighting (the cans are roughed in but oh well). The surface lighting you mentioned might work as wall sconces. The wall opposite the windows is around 5 foot 9 inches tall. I don't think we could give up any more ceiling height to flush mounts on ceiling. We might look at some sort of strip lighting on the window side -- I need to be creative here.

Now for my questions:

1) Is the blown fiberglass better R per inch than the dense packed cellulose that you and I discussed in another thread? Also, are these blown products both better than using a stack of rigid insulation? If the rigid insulation is as good per inch than the blown products were are all game to do those ourselves after the air space has been created as you planned. Installing rigid insulation in a between i-joists has been done by DH before as it was needed for our in floor heat.

2)I see your design would allow for the air space which the architect, I assume had planned via those purlins. We do have vented soffits (i.e. the soffits have holes in them). Do we need baffles too, or is the air space created by the ripped wood nailed to each side of joist sufficient (taken together with ridge vent)?

Thanks so much for sharing your expertise.

Carol

The specs called for R-42 batt insulation.

That's greater than the R-31 called for in all Compliance Packages listed Supplementary Standard SB12 of the OBC (Ontario Building Code) for ceilings without attic space.

Carol,

Depending on the pitch of the roof, I would specify for 1.5 - 2".

Several layers of rigid foam from there will give you a good thickness and R-Value.

After that, the insulation that you want to run is up to you. Blown in fiberglass (Spider) or cellulose will all work.

Worthy,

Glad to know we have exceeded the minimum code with what the architect spec'd. It would be very unlike him to have downgraded us. Thanks!

Washington,

Do you see any reason for us not to use all rigid insulation. With rigid we can skip the labour charges of either blown product. We are trying to DIY (mainly DH) the rest of the house build where possible. The pitch is 7.5:12. So what is the ultimate air space to leave? Thanks!

Carol

We need more information before attempting to redesign the roof system.

Until the architect explains the purpose of the purlins or we see the original roof plan or roof detail, we must consider that the purlins might have been for the purpose of allowing air movement between rafter bays at roof hips, dormers and skylights. Full bay insulation baffles could have been installed below the purlins allowing the free movement of air in all directions above the insulation.

Ont-
yes, rigid insulation would work in-place of a blown product. However it may cost you more if using XPS instead of paying someone to blow it in. But, if you create an air tight seal by the method I describe, you can put the r42 batt below the XPS vent and call it a day. After you stop the air movement through the batt, they will preform better.
As Worthy stated, you hit your no attic r values for your area, but IMO that is extremely low and I have never been one for shifting r values around like codes can allow. A roof is a roof to me, so I treat all spaces with the same r value. Codes allow for no attics or non-vents to be less r value then attic spaces. Never made sense to me. Then again I design roofs for r60 and not r49 too. In our area, blowing an r 60 cost dollars more than an r49. (about a $200-300 upcharge for 1500 sqft on average).

Hi all,

We have spoken to the architect. While he was not impressed with the framing error, he does see a reasonable solution. The purpose behind the purlins was to cross-ventilate. However, the architect said there is much debate as to how vital this cross ventilation is. Also the area is small so the concern of missing purlins is less of an issue. He did say if we run into issues with our shingles the warranty on this portion of shingles would likely be null and void due to lack of the intended cross ventilation purlins.

I was completely off base by saying the purlins were to run parallel to the rafters. Sorry for the confusion. They WERE to have run cross wise (perpendicular to the rafters) to allow a continuous cross venting between the roof sheathing and rafters due to a continuous space between sheathing and rafters. However, they are not there.

So, the solution proposed by the architect is very similar to what Izerarc proposed. We are to leave a 1 1/2 inch air space and then use one sheet of rigid between each rafter combined with 7 1/2' of batt insulation. We will either guard the air space by using the method described by Izerarc of using ripped lumber or just using friction fit with exact sized rigid insulation to preserve the airspace. The perforated soffits in this attic area is at the front of the dormer (window side) as seen in the real life photo.

So, tomorrow we meet with the building inspector to see if the architect's fix will do.

I appreciate you trouble shooting with me this weekend. If you see any issues with this plan please let me know. Let me know also if you think this lack of cross ventilation is a serious error.

Thanks everyone!

Carol

I would recommend not friction fitting. Have been there before, and its more work to rip the pieces, but you are assured your air space is the same width and the sheet foam can not be accidently pushed up at any point, such as when installing the batts or drywall.

Purlins always run perpendicular to rafters so your description was clear enough and cross ventilation was the only logical explanation for it but what is still not clear is the extent of discontinuous rafter bays due to the framing of hips, dormers or skylights. I guess all you can do at this point is drill some holes to allow at least some amount of moisture to migrate to the ventilated bays.

Lack of adequate roof ventilation has never been proven to be a serious cause of a premature asphalt roofing failures but some manufacturers have held on to that installation requirement because it is so effective in reducing the number of successful warranty claims.

But with the increase in unvented cathedral ceilings most manufacturers have either dropped the requirement or reduced the warranty period to 10 years and most also stipulate that inadequate ventilation will not void a claim for failure unrelated to improper ventilation. So, until you read your warranty it's not worth worrying about this issue.

It's good to finally hear from the designer of the project. I was beginning to feel we were approaching the point of poor professional ethics.

Izerarc,

I see your point about the risks of friction fit. Our framer said we could also put a few screws into the rafters (not the foam) where needed to keep the rigid insulation in place. Is that a viable idea?

Renovator,

I was glad DH reached the architect too. As an aside, I don't know if you recall our former garage gable roof on this house that blocked the small dormers? If so, you might imagine that we are not in our architect's good book now as we wanted to change his original design to a flat roof. It was hard for him, and hard on our budget. If you don't recall this issue, please disregard.

The architect said no to the idea of drilling holes in the rafters to allow better circulation (maybe he would have said yes if he made a site visit). It seems to make sense to the siding carpenter -- he liked the idea very much. I will see what the inspector says on this idea.

Thanks,

Carol

This post was edited by OntarioMom on Mon, Aug 19, 13 at 21:13

screw work, as long as you go with thick enough foam.
I like the wood mainly since it gives you a great place to create an air seal. anytime you can put down a bead and press something into it you will get the best air seal. Sick the foam up and then topical caulking the joint where it meets the rafter is not nearly as good.
They should have/would have needed to install the purlins if they bid per your plans, so installing the wood strips would be an even trade if I were onsight discussing it with them.

Thank you everyone for all your help and assistance. I really appreciate your time!

In an attempt to answer Renovator8's comment: "what is still not clear is the extent of discontinuous rafter bays due to the framing of hips, dormers or skylights", I am posting a picture of the size of the area. Keep in mind the ceilings are low as the photo of the area shows. The tallest parts are only about 5 foot 10 inches. The area is separated by LVL rafters in the middle. The framer noted that the bottom half of the area is more open to the regular attic so less of a concern that the top half (window side) in terms of venting issues.

Can anyone help me figure out how to light this attic if we remove the pot lights to improve R value? I was thinking we could do sconce lights on the bottom wall and perhaps one on the closet wall and on the wall opposite the closet. That would illuminate the bottom half of the area. The area near the window at night would be dark unless we can do some sort of strip lighting or low on wall wall washes like you see beside stairs?

Thanks again!

Izerac,

Thanks for explaining your rationale for the wood being better than screws. I get it now. Very good point that the original framers can put those strips of wood in at no cost to us and no labour to DH.

Today we discovered a bunch of other issues with poor attic truss backing/bracing in the regular, non cathedral attic area. We had the framing inspected by an independent inspector. I can't believe we passed framing inspection with the city! So those original framers are back for sure (hopefully at no cost to us to fix what they did poorly) and they can put those wood strips in the cathedral attic when they return.

Carol

I cant believe R31 passes minimum in a Canadian roof!? Maybe on southern Victoria Island but Ontario!? That is a very powerful and shortsighted home building lobby you have up there to get that pathetic loophole passed. Some local inspection departments do better than others but no one should expect them to be catching all the structural mistakes let alone important energy requirements.

Miami (US climate zone 1) 2012 IECC calls for R30. Ontario falls in us zones 6,7 and 8 with those MINIMUMS being R49. Yes, non-attic spaces and performance compliance allows less but R49 and higher is where you should be shooting for unless youre making it up somewhere else. Personally, I would be going for R2000, a canadian certification that may be pushing for much higher values. I found R80 referenced in the link below.

Most important is that any ventilation channel and ceiling plane is meticulously air sealed.Airtightness is almost always more important than R value because its almost always done poorly and leads to worse problems like rotting sheathing and ice dams in cold climate roof situations.

Izearcs tip about how to maintain a ventilation channel in an air tight manner is great. I would also have you get a bid or quote for doing spray foam as I find it to be comparable in costs to dense pack cellulose or FG in my area and it offers a much tighter air barrier. I think the headache and stinky foam concerns are overblown.

The best way for you to add R value at this point is running dimensional lumber, on edge, perpindicular to the rafters held in place with structural screws. This will decrease the substantial thermal bridging through the rafters. Layers of rigid foam is likely to be leaky, labor intensive and be a higher $ per R in material compared to other methods.

I think your sconces will work fine. Cove molding with led tape, rope light, or flourecent directed upwards works well too. You can always add floor and desk lamps. Avoiding recessed lights is always a good idea, especially in your climate.

Here is a link that might be useful: Future of R2000

Brian,

Thank you for your detailed response full of helpful info. We are in zone 6a (same zone as Worthy, I believe). It could be that different parts of Ontario have different R minimums as northern Ontario is sure a lot colder than here. However, I do agree that the code minimum is low for conditioned attic space. Our plan is to have at least R42 (one 2 inch rigid and the rest in a batt). So, while not perfect, we don't want to loose any extra ceiling height for higher R.

As per spray foam, we are all living in the house, so would have to leave the house for a few days minimum for the spray foam adding to our cost (no relatives close by). The architect does not want spray foam against the roof sheathing (he gave a reason to DH as to why I think it had to do with shortening the life of the shingles). One son has several allergies and has asthma that is severe. Others have suggested spray foam to us in this application so we have considered it, but don't feel comfortable going with it.

We are going to pay to get our other attic area blown. We will get a quote to dense pack the cathedral attic with cellulose or use blown fiberglass and compare $ for R with these various options.

Thank you for your lighting suggestions. Where do you see the Cove molding going?

When you said: "The best way for you to add R value at this point is running dimensional lumber, on edge, perpendicular to the rafters held in place with structural screws. This will decrease the substantial thermal bridging through the rafters. Did you mean we should use the strapping as described by Izerarc or large lumber on edge. Can you elaborate as you lost me here.

Thanks again, Brian for your help and link.

Carol

This post was edited by OntarioMom on Mon, Aug 19, 13 at 19:31

Thanks for being receptive and it looks like you are going to have a lovely home! Looking back at your original picture, I can see the concern with headroom and needing to settle with as-built rafter depth. Those reading this in the planning stages take note.

My thoughts were to run 2x4 (or wider) on edge below the rafters which would give you an additional 3.5" room for insulation but more importantly gets some insulation under the edges of the rafters which act as thermal bridging, degrading the effective R value of the roof assembly. Roughly 20% of your roof area will perform at R12 (the rafters R value) without such measures. I wonder if you could get by with a 2x2 (1.5" loss of headroom)?

If you follow Lzearcs good tip, you lose 3/4-1.5" of insulation from the presumed 11.25 rafter depth, leaving roughly 10" for insulation in the cavities. Assuming R10 for the 2" foam chute and 3.6R per inch for remaining 8" gives roughly R39. Adding my suggested 1.5" (2x2 below rafters) suggestion only bumps the CAVITIES to R44 but the effect of the roof assembly insulation is much greater because it changes the earlier 20% at R12 to R17. Foam sheathing below the rafters is another option but perhaps riskier from a building scientist's perspective.

Again, all this R value math is meaningless without a blower door test proving the home's overall airtightness. The 1.5 ACH50 in the R2000 is a much more important goal.

I think most shingle manufacturers have abandoned the ventilation issue and most research suggests that shingle color is a far bigger factor to degradation (lighter = better).

For lighting, should have checked pic before suggesting cove but I can envision a false ridge beam recessed from the ceiling to provide a shelf for the up lighting. Our code requires knee walls and it looks like the ceiling intersection might still work..

Checking that link again, want to point out that the upcharge estimate is for many upgrades from the perspective of a production builder seeking to resist anything that might increase costs and reduce profit margin. A builder already doing some of those things would probably not see such a big difference. I kind of wonder if the author might have played a part in the loophole that got me so worked up!

Brian,

Thank you much for your continued help with my project! It is too bad we can't do something about that loss of R from each rafter -- that is a substantial energy loss you noted. Right now in the centre of the room, and a few other spots, an average height female can stand up with head to ceiling. It we lose anymore than say the thickness of drywall, and the strapping spec'd to anchor the drywall to, I think we lose a lot of height comfort. Is there such a product that combines drywall with say some sort of insulation backing (for example a 1/4 inch foam or such). Otherwise, once we add the strapping crosswise spec'd by the architect to hold the drywall to, could we possibly just spray foam in between the strapping lumber directly on the edge of the rafters? A bit of foam like that should be able to be less of a concern with asthma, headaches, etc. Or does rigid insulation come in 3/4 inch thick sheets?

We will definitely get a blower door test before installing drywall. You may be happy to hear those windows in the attic area, and in almost every window in the house, are all triple pane fiberglass. We have 2 X 6 construction too in most areas (with 2 X 4 walls in some parts of the original house with insulation on outside). We also have ICF basement for the large addition. The cathedral attic area will be the weak link, but the rest of the house will quite energy tight.

I totally agree that builders should not turn their back on building energy tight homes for fear of reduced profit margins. Surely they can pass along the costs to the homeowners to keep their profits consistent. We are GCing the house ourselves, so there is no middle man concerned with profit here luckily.

Thanks for your added info on the lighting. I will see what we can design for cove lighting as suggested. That would be really cool.

Thanks again for your help!

Carol

While 9.9/10 Brian and I agree, I think this is also a unique istance where head heights are very limited. I think hitting r40 is going to be about the best you can get without getting deeper, reducing head heights, and going to closed cell foam. While I think you could probably manage to strap it with another 1.5", thats still a lot to take out of your ceiling.
I have spray foamed Ijoists in part of my ceiling. I was there when they were spraying it, and I can say there is some fumes, but not nearly what I thought they would be. They went away pretty quickly. Of course water was the blowing agent so that certainly helps. My build I did not do much to prevent thermal bridging in the roof line, however I did go with 14" deep Ijoists instead of solid wood to reduce it. There is only 1/2" of OSB connecting the outer wood flange with the inner, so thermal briding is reduced quite a bit. Filled full with open cell puts me right around an r50 for this area. Blown fiberglass attic area is an r60.

Here is a thought to handle lighting. I have done this before in a similar situation. I made a quick sketch so its easier to see. Bascially create a suspended shelf that creates a cove at the peak. install linear T5 fixtures on their side to shine down and out into the space. I would also recommend painting the ceiling a semi gloss or gloss white to help reflect and bounce the light around. I think you would be amazed at how much light this will produce for the space. You can also go with a double bulb T5 if you want even more. I would suggest going with the double bulb and putting them on dimming ballast then you have a lot of flexibility. However the dimming ballast does add quite a bit. A typical, unfinished (no fancy body on the light) 4' T5 fixture will run you under $20 typically each.

You are getting some good advice Carol. These guys know their stuff.

I would not be concerned about the warranty on the shingled roof. If it is ventilated, it is ventilated.

If you do a good job of sealing the rigid foam barrier to create the vented space, virtually no moisture will be making it to the roof deck and given your location, the heat is not the biggest issue to the roof.

The only think flawed in the roof design will be the thermal bridging of the framing members where that would be lessened with the purlin approach.

As far as the insulation schedule, be sure the rigid foam is sealed up tight and the seams between the framing and sections are detailed right. This is where some sprayable sealant or spray foam would be helpful.

Also, if the framer dropped the ball, I might just specify some Spray foam for those sections (after the rigid foam) and call it a day.

You can do it with batts as mentioned above, but the SPF will help with the air barrier details and just does a bit of an easier job...doing its job...in ceiling applications.

If not SPF, blown in fiberglass or cellulose work well.

Be sure to have the drywall done airtight (ADA - Airtight Drywall approach) so that no moisture is making it into that assembly.

Happy insulating.

Thanks guys (I think you are all guys that is),
Izerarc,

That is a nice hall ceiling room you have with spray foam. I love the high windows. You were smart to use i-joist to reduce thermal bridging.

Thank you very much for the lighting diagram. I will look into the idea of cove lighting some more as this is intriguing. If I am understanding you correctly we would have to lose a few inches at the ridge for this style of cove lighting, correct? We will paint it semi-gloss of high gloss as suggested. I am sure that ceiling will get dirtier than most given the low head room. Love the extra light benefit too.

WOW,

Thanks for your insights and tips. We will learn more about ADA to get the drywall done right. Is SPF spray foam like Great Stuff? Good to hear you don't think the shingles are in danger of premature wear.

Carol

Great Stuff is SPF but not in the capacity that you would be needing it. Great Stuff is a 1-part SPF if you are referring to the canned foam. They do sell Froth Paks but the yield and quality of installation are terrible as compared to a proper spray foam rig and installer.

You would have a truck and rig deliver and install the foam.

They mix the part A and part B on the truck as they are heated and run through a reactor.

Update:

The inspector is insisting we need to leave 2 1/2 inch airspace on this short attic cathedral. The depth of the rafters is 11 1/4". That will limit our options if we want at least R40. We are not keen on spray foam (except in a very small quantity to fill cracks/gaps etc). Can we do two sheets of 2 inch rigid insulation plus batt? Our architect would be content with less R (code minimum R31), but that does not sit well with us.

Worthy, the Ontario building code the inspector is insisting on is section 9.19.1.3.

Any more thoughts? Can we use two sheets of rigid and the rest batt? We don't want to lose any more headroom as it is extremely short already. Should I go to dense pack or another kind of blown insulation?

Carol

It's helpful to know the code requirements and unfortunate that the builder was not familiar with them and did not follow the contract documents. Your builder and architect should have already presented you with all of the possible alternatives. One alternative should be to remove the non-complying work and building the roof as required by law and the contract.

Section 9.19. Roof Spaces

9.19.1. Venting

9.19.1.1. Required Venting
(1) Except where it can be shown to be unnecessary, where insulation is installed between a ceiling and the underside of the roof sheathing, a space shall be provided between the insulation and the sheathing, and vents shall be installed to permit the movement of air from the space to the exterior.
9.19.1.2. Vent Requirements
(1) Except as provided in Sentence (2), the unobstructed vent area shall be not less than 1/300 of the insulated ceiling area.
(2) Where the roof slope is less than 1 in 6 or in roofs that are constructed with roof joists, the unobstructed vent area shall be not less than 1/150 of the insulated ceiling area.
(3) Required vents are permitted to be roof type, eave type, gable-end type or any combination of them, and shall be distributed,
(a) uniformly on opposite sides of the building,
(b) with not less than 25% of the required openings located at the top of the space, and
(c) with not less than 25% of the required openings located at the bottom of the space.
(4) Except where each roof joist space referred to in Sentence (2) is separately vented, roof joist spaces shall be interconnected by installing purlins not less than 38 mm by 38 mm on the top of the roof joists.
(5) Vents shall comply with CAN3-A93-M, âÂÂNatural Airflow Ventilators for BuildingsâÂÂ.
9.19.1.3. Clearances
(1) Except as provided in Sentence (2), where venting is provided to a roof joist space, not less than 63 mm of space shall be provided between the top of the insulation and the underside of the roof sheathing.
(2) Where venting is provided at the junction of sloped roofs and exterior walls and where preformed baffles are used to contain the insulation, the baffles shall,
(a) provide an unobstructed air space between the insulation and the underside of the roof sheathing, that is,
(i) not less than 25 mm in dimension, and
(ii) of sufficient cross area to meet the attic or roof space venting requirements of Article 9.19.1.2., and
(b) extend vertically not less than 50 mm above the top of the insulation.
(3) Ceiling insulation shall be installed in a manner that will not restrict a free flow of air through roof vents or through any portion of the attic or roof space.
9.19.1.4. Mansard or Gambrel Roof
(1) The lower portion of a mansard or gambrel style roof need not be ventilated.
(2) The upper portion of roofs described in Sentence (1) shall be ventilated in conformance with the requirements in Articles 9.19.1.1. to 9.19.1.3.

Thank you Renovator for posting the actual code. We are still undecided what to do, but will likely not ask the framing subs to rip apart what they built and rebuild. I know we could though.

Carol

Hi all,

I wanted to give you an update, and also share with you the latest concern DH has been given about this tricky insulation area.

We decided to use five layers of rigid insulation (XPS) (four layers of 2 inch and one layer of 1 inch) in each rafter bays. DH and son carefully fitted each piece of rigid insulation and left the code required air gap under the roof sheating (2 1/2inch).

On Friday DH had an insulation contractor out to get a quote on a few other house areas and to get him to quote on spraying the gaps in between the rigid insulation with foam. The insulation contractor was most concerned with the work that had been done. He felt the air gap would get very hot and over heat the shingles as well as the lack of ventilation would cause rot in the rafters. He was recommending that DH rip out all the rigid insulation and start over this time using only spray foam!!!!! The insulation contractor basically said what was done will not work and we needed to go back to square one.

We will be getting more opinions next week from other insulating contractors and I am encouraging DH to call the structural engineer for his opinion. Of course, the insulation contractors would all love to sell as the service of foaming the attic area, and in my mind might possibly even be motivated to cause panic with what has been done (rightly or wrongly is what I am unsure of).

Here are my questions now:

1)Is there truth to what the insulation contractor stated (i.e. that the moisture in the area would rot the wood rafters, the room would over heat and that the shingles would over heat as well)? We only have a ridge vent and no ventilation between the bays (just the air gap).

2)If we stick with the rigid insulation work, what kind of foam should we be using in the gaps/awkward spaces that were hard to cover with the rigid insulation?

3)If we stick with the near completed rigid insulation (and foam in gaps) do we use a poly vapour barrier?

Here are some pictures of the area under construction.

Carol

Thanks in advance for your advice as DH is rather heart sick at the possible error and possible waste of time and money.

your DH put in a lot of hours on this install & did a nice job.

code dictates an air space, according to your post
above & the code provided by Reno8.

foam companies want to make the most money possible per job. comming to your site & setting up for pennies on
the dollar as compared to same set up time for full roofline
install of foam has a lot to do with the advice you recieve.

check with your code inspector as to what has been done
by your DH to date. explain what was told to you by foam
company.

I'm not a cold climate expert, so will of course defer to those who are.

the afore mentioned froth packs might be what you'd use to seal around the foam sections. per can cost of great stuff would be very expensive. is closed cell or open cell used for your climate? froth packs come with both.
some learning curve would be needed to learn technique for spraying te foam, so include that in your order & schedule.

btw...in the last picture, to the right of the dormer...is that a stove vent pipe? or what?

best of luck & congrats to your DH for being so hands on.

Hi energy_rater,

Thanks for your words of wisdom and I will pass along your kind comments to DH and son (they could use them after Friday's comments from insulator). I do hope the panic created by the one insulator was over blown. As per the froth packs mentioned by you and others, do you have a brand name for these? Is it something that DH can do, or do we contract it out? I know closed cell is used in our area, and not sure about open cell.

Should DH use a vapour barrier (poly) after using the foam in the gaps?

As per the pipe, there are two of them that run through this kids attic area. They are Sun Tunnels and they bring light to 2 windowless baths below. We have plans to protect them before dry walling around them. We will likely paint trees on them for whimsy in this kids area.

Thanks again for your comments!

Carol

this is what my SO used at his son's home in
indianapolis, with good results.

http://www.tigerfoam.com/

hope this helps!

Thanks energy_rater!

Did you SO apply the tigerfoam himself or get an insulator to do it?

Carol

he started it to show his son how to apply it.
then son finished job & has since foamed
rim joists & band joists.

there are quite a few videos on you tube
showing how to use these kits.
just remember...if it gets on your skin
it has to wear off.

goggles, gloves, face mask & tyvek suit
recommended.

Thanks energy_rater,

I will see what DH says about learning to DIY the foam needed. Would you recommend the fast rise or slow rise formula from Tiger Foam?

What do you say about the vapour barrier (poly) given most of area is rigid insulation and only gaps with spray foam? Yah or nay to a vapour barrier?

Carol

I'll ask him what they used & get back to you.

as for vb..in my mind the vb is the foam sheathing...
but I live in a hot humid climate so hesitate
to give you an answer for your cold climate.