I offer him sympathy at the thought of making his job "more difficult" even though that's an attitude and not a reality. OTOH, he really should learn what is involved with spray foam insulation -- and you can tell him you won't charge him for the learning experience! Yes, there are after-the-fact spray-in foams, but there is no reason to try them in this situation. I think the plumber is pushing his luck because few if any properly constructed new houses install showers etc until AFTER the insulation is put on. There is no way to be sure the insulation is solid and without leakage after the walls (or shower walls) are installed.

I've found that rooms over garages are very hard to condition. there are a couple of ways to address this, walls shared with attic space are called kneewalls. on one side is living space (conditioned) on the other side attic space (extreme heat/cold). Southface has great info, check page 5 for visual of air sealing these walls. http://www.southface.org/default-interior/Documents/airsealingkeypoints.pdf with these attic rooms surrounded on 6 sides by extreme attic temps there are two ways to address them. one is pictured in link. convnetional insulation in stud bays, foam sheathing, caulked nailed & taped in place from top plate to bottom plate of kneewall. the detail on link also shows how to seal for air movement under floors of these rooms by using foam board, and placing it between floor joists & sealing air tight. I personally like to cut the foam board to fit tightly & air seal with caulk. I see people using great stuff..but am not a fan of the stuff myself. too much expansion to get a good seal, and over time, it shrinks. this is a process that is time consuming & detail oriented. easiest in new construction prior to any insulation being added to attic floor. more cost effective than spray foaming the walls and between floor area. but labor intensive. so its a easy fast process (spray foam) or a longer lower cost higher labor install with foam board. the benefit of creating an unvented semi conditioned attic space works great in my hot humid climate where in the summer attic temps reach 130+ degrees in attics. as we often put our ducts in the attic, the foam creates a less extreme temp for less heat gain. install of foam is crucial. temp mix has to be correct chemical mix has to be correct, temp of area sprayed is a factor. foam has to meet code requirements for your area. if code says R-30 in attic, enough inches of foam to reach that R-value has to be installed. seal has to be complete in an unvented attic. roof connection to attic floor has to be sealed. install should be level, no belly in or out between rafters. faces of rafters should be covered. none of that average fill stuff which means the spray can be less in some areas & more in others so that it 'averages' out to xx inches. low spots & voids will cause problems. testing for leakage, marking leakage sites with spray paint and having foam company spray to seal is the way I do my unvented attics. this all has to be established, in writing prior to any work being done. shop companies carefully. avoid 'average' fills, Kvalues Qvalues. R-values that is what code looks for. there is No exception for spray foam. I'm with Manhatten all the way on spray foam in walls. long payback when a better option is to put foam sheathing on exterior of walls & pay close attention to air sealing details. search southface site for air sealing pdfs..great stuff there! I've never recommended spray foam in walls after running the numbers for my climate & seeing 25+ year paybacks. and I've done these numbers lots of times, not just for one house. (btw hey Manhatten..long time no see) if you chose to use these details of air sealing for the tradeoff for this better insulation is SMALLER hvac system. it only makes sense people if you weight the benefits of upgrades against each other. get a load calc for the house including all types of insulation, window info, air tightness tight not leaky or average & the size needed lessens. bigger is not better, it is just lack of correct education in the trades & misinformatin to the homeowner to sell them more equipment than needed. you don't size the system for the 10 days a year of 50 people in the house & then pay for that the other 355 days. two stage units, variable speed air handlers are great things that vary with the needs of the house as they change. these are good investments. if you are truly interested in making your house efficient, hire an energy rater. specific to you information with inspections, testing & verification. unbiased working for you. resnet.us is a good place to start. new construction, existing homes we do it all. best of uck.

I guess I'm still confused on your layout. Based on the above I believe you are saying... Lowest/1st Level - Basement - underground - 700 sq ft. 2nd Level - Ground level - 700 sq ft. 3rd Level - 1,400 sq ft. 4th Level - 1,400 sq ft. Is the above correct? If so, several questions... 1. Which levels are finished? I'm assuming the basement will not be finished or the assumption is it does not need cooling since there will only be a return & no supply. Regardless, that is a bad idea. If you have only a return & no supply & if you have a tight house, theoretically the basement will turn into a vacuum. 2. Adding up 2 levels of 1,400 sq ft & 1 level of 700 sq ft equals 3,500 sq ft, not 3,300 sq ft. Why the difference? 3. It must be a very unique house design to have a 700 sq ft ground level footprint but then supporting an area twice that large above. You can't cantilever (actually I guess you could but it would be a very expensive solution) that much so you must have additional footings & piers around the 1,400 sq ft perimeter. Can you post pictures of the house or design? 4. The "cost" of a 2 1/2 ton versus that of a 3 ton is actually quite small. A contractor may elect to "price" it much more but in a competitive market you typically would not see that much of a difference in the "price". I think the primary reason people oversize is to be sure it can cool the house to the desired temps regardless of the outside temps. He is right regarding the mold & mildew issues so you would be better off with a slightly undersized unit & live w/ a few days a year when it might not cool to 68 degrees when it is 100 degrees outside. You can play with that number with the Manual J variables to see how that changes the tonnage specifications. Personally, I used 94 degrees in my area even though we do have several days a year when it hits 100 degrees. Part of that reasoning is at night we like it around 68 degrees inside but obviously the outside temps are much lower at night. So be sure to use the desired inside temperature @ the time the outside temps are hitting their highs. In our case 75 degrees inside is fine during the day. What area of the country do you live in? 5. How much window coverage do you have? What is the U-factor of those windows? I'm actually surprised that is the Manual J was done that it does not suggest the need for larger unit for the top level. You would not input any heat gains/losses for the ceilings of the basement, the ground level, or the 3rd level (1st 1,400 sq ft level) since the areas above would be "conditioned". However, you would input the ceiling/roof heat gains/losses for the 4th level thus it should have a higher BTU gain/loss than the 3rd level. Maybe it just was not quite enough to trigger to the next size up. Ask to see the numbers & if the 3rd & 4th level are the same then there is something wrong, unless you have a lot more windows on the 3rd level than the 4th level.

Funny you should cover the K&T issue. We didn't want a house that had it, because of the issue of it been dangerous, particulalry with insulation, which we need up here. When we bought the 60 year-old house the folks selling it claimed everything was fine and dandy with the wiring. There was some K&T in the basement, which we asked them to remove, and they only sort of did - removing it right to the edge of the basement. Turns out this was because the whole house was K&T and they knew we wouldn't buy the house if we knew. Anyway, when we had a remodel done, the electrician told us about the true extent of the K&T and we had it all replaced. So in the end, K&T is now not an issue. Although those darn sellers knew that they were tricking us when they "forgot" to tell us about it and only did half the job when they "removed" it from the basement! Cheers