Insulate attic by adding fiberglass to top of plywood floor?
locust78
13 years ago
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baymee
13 years agodedtired
13 years agoRelated Discussions
Fiberglass Insulation: How Do I Cover the Attic?
Comments (3)Solargary, thank you so much for your reply. Very helpful. I did not know that DIY blow insulation is that easy.... My house is about 1400 sq, and where I can stand is almost on the left edge. Do you think that the blow machine still can shoot out the insulation that far (about 35 feet away)?...See Moreair sealing attic...move plywood?
Comments (6)putting foam sheathing doesn't do anything but insulate the storage area flooring. it is a waste of time money and effort. in adding foam sheathing you are adding a vapor on top of the batts/blown insulation. batts actually work better on slopes because it is the uniformity of the insulation. as you will see, the blown will vary in depth in this area. it would behove you to get up into the attic before they finish and take a look. ask the R-value per inch of whatever blown insulation they are installing. figure out how many inches need to be in place to achieve this quoted R-value. take a yardstick or some form of measurement and measure the depth of the install in several areas. or ask them to do it while you shine a light to see if the depth is reached. any low spots should be filled. blown settles so depth should be a few inches over quoted inches. types of insulation have different qualities so some compacts (settles) more than others. if they are using cellulose..the air sealing is more important than ever.cellulose has a fine dust that will enter thru the smallest of areas. the bath fan for instance has openings in the housing. the cut where it fits thru ceiling is oversized. this cut should be sealed with mastic tape. back draft damper should be properly installed and vented out of insulation..perferably out of attic. the sloped ceiling is another place that will de-rate the overall R-value of the install. as are each recessed light (1 unsealed IC light = 1 sq ft of uninsulated attic space) you can see by the dirt on the batts how leaky the can lights are. if they don't address them from in the attic you may be able to install an ICAT insert and trim from inside the house. expect to pay $15 for insert, plus trim. you will need to brand name and model number of the recessed light. once you retrofit them use cfl's for more savings. if the attic is 1200 sq ft, and bid is for 944 sq ft, then 256 sq ft is the storage... I guess. I don't know what your starting out R-value is or what they plan to install. but as an energy rater (note rater not auditor) we have to deduct for areas like sloped ceilings, recessed cans, storage areas and all areas that have less insulation than overall. the attic staircase when not properly sealed and insulated derates the insulation install, and air leakage from this and recessed cans further are also penalties. I'm learning that these are some of the many differences between raters and auditors..and when utilities are involved in providing work for auditors and incentives the quality of the audit/rating is in question. if some company is paying a portion of your fee, you are not unbiased and working 100% for the homeowner. I've found hvac companies to be bad at sealing their own work.. best of luck....See MoreInsulation - remove paper on fiberglass batt in attic install?
Comments (13)Thanks Ionized, Energy_Rater and Mike_Home, As there is no compelling reason to remove existing insulation, it seems best to leave what's there in place. But the kraft paper has to be removed. These are R-values for the two products: Fiberglass, 2.2 to 2.7 per inch; Rockwool, 3.0 to 3.3 per inch. Using the median number of both, I estimate the current installation's R-value at 16. CURRENT INSULATION'S R-VALUE Fiberglass: 2.5R x 4" = 10 R Rockwool: 3.1R x 2" = 6.2 R To get up to 30R, another 14R is needed which is: 5.6" of Fiberglass or 4.5" of Rockwool. So, laying one batt will get close to 30 R which is adequate as Mike suggested. Is it OK to lay Rockwool on top of the current fiberglass (after the paper is stripped off)? Below is a link on how to dress for installing insulation. Fiberglass asks for more dress-up than does Rockwool...a different sort of date. ;-) This same website provided the R-values in the article on "How to compare f/g and r/w". Gosh, you've all been so helpful. I am very grateful. Thank you. Here is a link that might be useful: How to Dress for Working With Fiberglass Insulation...See MoreAttic, Insulation, and Top Plate sealing
Comments (1)Attics should always be vented. The purpose of the ventilation is allow moisture to escape. If moisture is trapped you could have a mold problem. Since you have the soffit vents, a roof contractor may be able to add a ridge vent. If that is not possible then adding so other types of vents should not be difficult. The soffit vents take in the air, but you need vents near to the peak allow the air to exhaust. You want the attic to be as cold as possible. This will prevent ice damming in the winter. The insulation on the floor is what keeps the house warm and cool, not the roof deck. The insulation should be at least R30, and preferably R38. More is always better, but you don't have to get carried away. You quickly hit the law of diminishing returns. Sealing is good, but I am not sure how much of a pay back it brings. Air can still flow through the loose insulation so adding more on top does nothing for sealing. I don't see the need to wait. You have about an R-13 to R-19 insulation rating now. I suggest getting some quotes and having it done in the fall when temperatures are mild....See Moredavidro1
13 years agoccintx
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13 years agodavid_cary
13 years ago
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