Adding Attic Insulation With Poor Vapour Barrier

[JFoy]

There is an Ad on the radio for fiberglass windows that drives me nuts. They claim "your house is insulated with fiberglass, so your windows should be too" Talk about misleading. We have had good service from our forty year plus, vinyl windows. With the exception of some thermopane seals, but not the fault of the vinyl.

Last year, I dove into house planning and research as my wife and I wanted to build a new house. I had a huge list of 'great ideas' for an energy efficient house and started talking to everyone from energy auditors, general contractors, etc. What I ultimately learned was that sealing up a house against air intrusion was more important than insulation in terms of efficiency and comfort. The flip side was that sealing up the house too much meant it wouldn't breath and we would have to install a fresh air exchange system. So it can be overkilled in terms of tightness but what we'd save due to tightness would then be spent on running the fresh air exchange system. So, a balance is needed.

As far as fiberglass windows go, what I learned was that materials have a Coefficient of Expansion (CoE) which dictates how much they expand and contract based on temperature. A high CoE meant windows would allow air drafts to come in when they shrunk in the winter as gaps would form around them. Vinyl has a much higher CoE than fiberglass. So, a fiberglass window is a better choice for windows though they obviously cost more than vinyl. Again, we were back to the cost issue - the windows cost more but the monthly savings are greater so we're back to the balance game.

On the same note, I did an analysis of the significance of U=0.25 cheap windows versus U=0.17 expensive windows. I did a spreadsheet comparing the heat loss of the surface area of the windows versus the rest of the R-30 wall. What I realized was that the windows would cost me a couple thousand more and the savings based on our electric kilowatt/hour price was less than $100/yr - not worth it. So, fiberglass might make sense, but U=0.17 or less was a waste of money.

Hope that helps,
JFoy

 

[Larry Caldwell]

I replaced my 25-year old wood double-pane windows with worn out with falling-apart sashes and rattling triple-track storms with new big name brand vinyl clad wood low-e, and no storms...the old system seemed to be less drafty. Say what you like, it's hard to beat a 2" air gap between the sash and storm window for knocking a draft down to almost nothing.

I installed the windows myself, and foamed them with latex foam, so there are no drafts. It also only cost me $1600 to do the whole house, including a 10x5 in the living room, six 5x4 and two smaller occluded glass bathroom windows. Replacing the doors cost more than that. Replacing the old slider with high quality Pella French doors and the entry door with an insulated wood over fiberglass also made a huge difference.

Insulation - the gift that keeps on giving. Installation is critical.

 

[Larry Caldwell]

We didn't get replacement windows at least, we did full new construction windows by going all the way out to the RO and then cutting back the siding a tad to fit the new trim. That allowed us to also improve flashing and replace water damage from the old windows that were so far gone as to allow water straight through --why put a new vinyl sash in a old leaky (air and water) wooden casing? I gained glass area in the same RO, in-casing replacements would have cost me air and light.

We also swapped out a pair of casement picture windows with sash bow windows, but I also know the insulation in those is not as good as I would have liked...I would have preferred to slow down a little to fuss over some of the details, but I was the "helper" to a buddy who was showing me how, so took what I could get. And yet I still get the knocks on my door and the fliers in my mailbox from guys who want to replace my NEW windows for 10x the cost. Um...guys?

That's the way to do window replacement. The fly-by-night window salesmen want to just sawzall out the old sash and stuff vinyl in. That just leaves a leaky mess. I pulled my old windows completely out and replaced both the interior and exterior trim. I also replaced a dinky 2x2 over the kitchen sink with a large bay window that is 6' wide. Even with low-E glass that one is inefficient because it sticks out past the shade of the house overhang. It gets pretty warm in the summer. I should probably stick reflective film on the outside.

 

[teejk]

Don't know how much foam your looking for but that number does seem like it could possibly be low.
He is probably very busy right now.

It is not a big house and I expect them to be in and out in a day. Foam in the fully exposed basement sill plates probably 1/2 hour...crawl space in a breezeway addition (funny thing about houses up here and the tendency to have detached garages only to connect them later) maybe an hour...adding a few inches of blown-in maybe an hour. It's a "cape style" house with "hidey hole" storage dormers in the upstairs bedrooms...foam. Cutting in a few roof vents...dunno...the lady has the money...if he low-balled (which I'm sure #1 did and that's why we never heard from him) he could admit that and we could take it from there. Starting to think that insulation pros are like the drive-by asphalt guys.

 

[GLyford]

That just leaves a leaky mess.

Well, to be fair, even with the windows foamed into the ROs, the whole rest of the wall is decidedly porous, as we found out when we added a porch off the dining room (now combined with the kitchen).

The rosin paper under the clapboards has a ton of holes, no blocking where the sheathing meets over the stud bays, they never folded the paper flaps out on the batts over the studs, and there was no other vapor barrier unless you count paint.

Since I had the first floor back wall apart anyway inside and out, I put up tyvek and a vapor barrier. Replaced a slider with a hinged door+sashed window to get another base cabinet in, plus the aforementioned porch and a full gut inside since we removed a non-load wall and replaced plumbing in the walls and ceiling. I had to relay the clapboards to match the new door/window openings and tie in the porch, which meant I could tyvek under them without much more work. Doing that (just the back half of the first floor) did knock the drafts down quite a bit. But I don't feel up to gutting and residing the rest of the house to do that everywhere else.

Even with low-E glass that one is inefficient because it sticks out past the shade of the house overhang. It gets pretty warm in the summer. I should probably stick reflective film on the outside.

We have an 85% shade sail we sometimes use over the back door + kitchen windows, have been debating putting up or not, but I think I will as soon as the July/Aug doldrums hit. Right now the night breeze is enough to cool the house off if we shut the windows in the morning.



You know, since this whole conversation is about attic insulation and not windows (in theory anyway), I ought to mention I need to roll out the R-19 batts I put up in my attic 2? 3? years ago to double what I have up there...they're still just sitting there. Also need to jam those foam vent baffles into the rafter bays so I don't block the soffit vents off. If I didn't already have that up there, I'd be really tempted to rent the blower and use the bagged shredded fiberglass...