seeking advice on improving the insulation in my house.

[Archer39]

I have a 2000sq ft bi-level that was built in 1976. Currently there are two layers for r-13 in the attic. The attic has 2x10 joists with a plywood floor nailed down in the center of the attic. The attic is used for storage. The current insulation is under the plywood in the center.

On one side of the plywood i have 87" of space from the soffit to the plywood and on the other i have 60". would i see any gain in heat retention by adding a layer of r-30 to these two outer edges?

I am going to remove the floor down the road and add a layer of r-30 to the whole thing and not use it for storage. But in the mean time i would like to improve my current insulation.

 

[Swedishchef]

Heat escapes from the weakest point (less insulated) in the system.

Is there ANY insulation on the sides of the plywood ( you said "The current insulation is under the plywood in the center.")? If there is none..add some! If there is already some well ipad little extra would not hurt. You may see a little extra retention but perhaps not as much as you would expect.

Ether way r26 isn't that much and it has likely settled over the years ( a bit...). I would certainly start putting some everywhere...sides and under the floor.

Andrew

 

[Archer39]

Yea, the entire attic is insulated. Not just under the plywood.

Would the insulation be as effective if I were to lay it right over the plywood floor as opposed to removing the plywood and adding it over the existing insulation ?

 

[woodgeek]

The bigger issue than insulation is airsealing. Right now, a huge amount of heat is leaking through your attic floor through various large and small holes. That air flows right through the insulation, so adding more insulation without airsealing would be a total waste that would not save you energy.

Fortunately fixing this is a pretty easy DIY with lots of info on the intertubes: http://www.greenbuildingadvisor.com/blogs/dept/musings/air-sealing-attic

This sort of airsealing is perhaps the biggest and most cost effective energy improvement most homeowners can do. In my 1960 house, DIY attic airsealing reduced my heat usage by >20%. Upping the insulation to R-50 only saved me ~5% and cost a lot more.

A lot of posts on here about folks doing this. If you go DIY, get good equipment, valved respirator, powered caulking gun, can foam gun, etc.

I opted to keep a decked area for storage. If there is (good shape) insulation and no air leaks under the decking, the energy loss, say from reducing R-50 to R-25 in that area is surprisingly small.

 

[Archer39]

It is pretty airtight in the attic. I have spent a good deal of time up there looking for and fixing leaks. There are still a few around the access door and a vent that need to be fixed.

Thanks for the info.

 

[woodgeek]

In my case caulking the framing top plates in the attic floor gave me most of the benefit, but was a PITA. The heat leaking through your top plates is almost certainly greater than the heat going through your current insulation. Sounds like you got the big holes, but in my case a <1/8" gap between the plate and drywall, times something like 200' linear feet of gap, added up to a HUGE opening.

As for the insulation, lets look at typical numbers...

Say your attic is 1500 sq ft, and R-25. Your BTU loss is DeltaT * area / R-value. When is is 30°F outside, that would be 40*1500/25 = 2400 BTUs/hr

Seasonally, the formula would be Area*HDD*24/R-value. Lets say you Heating Degree Days is 5000. The formula comes out to 7.2 Million BTU, $100-200 per season (depending on whether you had cheap or expensive heat (gas versus propane/oil)). Going from R-25 to R-50 would cut that in half, and save you ~3.5 MBTU, $50-100/year, or half a face cord of wood.

BUT, in old construction heat loss from air leakage at the top plates is probably 2-3X greater, with correspondingly higher savings.

 

[Archer39]

That's some good info, thanks a lot. I guess it's time to get up the with the caulk gun and look for all the little leaks now.

If I'm thinking of this correctly, the gaps at the top plates that you speak of would be around all the outside edges where the plaster (plaster walls and ceiling) ceiling meets the wood top plates?

 

[woodgeek]

yup. drywallers leave a little expansion space. depending on the installer, it varies in width. Some folks like to use spray foam, I used an 'attic rated' 100% silicone. You can research the merits of both, I personally don't think it matters much. My gaps were VERY dusty and dirty, and I brushed them thoroughly to get some good adhesion. Took a god-awful amount of caulk, like 15-20 tubes. Wished I had gotten a powered caulking gun after the fact.

My interior wall and gable end exterior wall top plates were straightforward. I had some pros do the top plates under my eaves, I couldn't reach them in my low pitch roof.

 

[Archer39]

Ok, thanks for the info.

 

[kingquad]

(broken link removed to https://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_seal_insulate&s=mega)

There is some very good free info in the link above. Bruce Harley's book "Insulate and Weatherize" is a really good resource too.

 

[Archer39]

I got up in the attic today to look for the gap at the top plate. I pulled up the insulation between 4 of the rafters and this what they looked like. Not much of a gap there.

Should I be concerned with it?

Also I was wrong with my original post stating there were 2x10 joist. They are only 2x6 and there is only 6" of insulation up there. I could not find any r-value on the bats. So I guess I have either r-19 or r-21.

 

[Swedishchef]

insulate away!!

 

[woodgeek]

I guess that is an exterior plate....tar paper and exterior sheathing. What do the interior wall top pates look like??

 

[Archer39]

unfortunately i can not get to any of the interior wall top plates. They are all in the center of the house and are all covered up by the attic flooring.

 

[woodgeek]

I was in a similar situation. I used an IR thermometer (scanning slowly and repeatedly) to determine that the decking immediately above my interior top plates was measurably warmer than the decking elsewhere.