Attic insulation

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Posted by: from Kirkland
4/22/2012 at 9:15:22 AM

Currently own a Grilli home build in 1981, split level with two roofs about 2000 sq feet total. Vents & soffits are adequate & up to code.

Problem; Condensation on inside roof plywood, as a result turning black, also house gets very warm in summer and cold in winter. I currently have about 12in of yellow insulation above my ceiling ( in attic). I recently discovered that my bathroom fan wasn't connected via the attic to the exterior. in other words fan would simply blow into the attic during hot showers. (i think this is why i have the black on my roof plywood). in addition to inadequate insulation.

Question; after repairing the connection from my bathroom fan, do i simply add more insulation to the attic or do i remove the current insulation and spray air tight insulation instead???

Also looking for someone reputable to do the job properly.


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Robert from Electrilight Ltd. in Oakville
Date/Time4/22/2012 at 10:42:28 AM

Sometimes you can never have too many vents in your attic... The black mould will not go away with it being treated and will eventually (years) ruin the plywood on the roof.

To prevent further damage, you have done right to get that exhaust as horizontal as possible to the outside. minimum insulation would be 16" to work properly. You can get a company to blow in another 12" on top of what you have quite cheaply or rent a machine and do it yourself.

Ensure you have soffit venting to match roof top venting so air can flow convection style from low to high and dry out the attic.


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Date/Time5/4/2012 at 11:54:16 AM

Hi Karim,

Robert is dead on with his comment.

First things first get the bathroom vent venting to the outside and tape all of the joints in the duct work, then wrap the duct in insulation (more is better). This keeps the cold winter attic air from condensing on the warm duct after a hot shower.

Next make sure that all of your soffit vents are 1) actually there, 2) clear of all obstructions. This is a common problem, especially if you have had cellulose of fibreglass insulation blown in and they did not temporarily block off the soffits. The rafters should be vented to a point higher than the insulation. The key being that air must be able to flow along the underside of the roof sheathing. This drastically improves drying of the wood and helps reduce temperatures of the substructure in the hot summer months which can contribute to early failure of your roofing.

Also, before you add insulation, and yes it is completely fine to add on top of your existing insulation (however account for compression when the new insulation is added), wear a respirator and long sleeves and tape the sleeves and the cuffs of your pants before heading up there, but brush away the insulation from the tops of ALL of the walls. Once exposed, locate all of the plumbing and electrical penetrations, then seal them ALL with spray foam, caulking, or best is red fire caulking. Your home leaks a tremendous amount of moist warm air into the attic from these penetrations.

Cut some plywood strips to surround your attic hatch as the required insulation thickness will far surpass the height of your ceiling joists.

Then add the insulation. You can use a variety of types but we recommend cellulose as it is treated with borate which prevents insect and mold damage and is far more fire retardant then the blown fibreglass. Check with the manufacturer to determine depth. Normally for R-50 you need 18" applied which will settle to somewhere between 15 and 16" after a short while.

Lastly, buy and apply some peel and stick insulation tape to the perimeter of the attic hatch and glue several layers of rigid foam insulation to the back side of the hatch. Try to achieve R-50 and make sure the adhesive you use is compatible with the foam insulation as the wrong types will melt the foam.

Best of luck.

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