Background:
I’ve decided to reside my home instead of repair and repaint. After making this decision I asked the contractor for a line item bid on a second layer of foam board. I currently have 1/2″ foam board in the non-shear zones and only 1/2″ OSB in the shear zones. The bid came back to install 1/2″ tongue and groove foam over everything for $2480. However, the contractor didn’t feel comfortable with nailing the new Hardie siding through 1″ total foam with the potential of missing studs, so he intends to use 1×2 backing at the studs and friction fit the foam in between for an additional $1960. That makes the total foam upgrade come to $4440.
Additional Information:
- two story 2400 sq ft located in northwest (Boise, ID)
- winter lows around 10 F; summer highs around 110 F
- central gas heating with highest winter gas bill around $250
- cenral electric air conditioning with highest summer electric bill around $130
Energy Savings Question:
Does anyone have hard numbers on the savings gained by adding more vertical foam board? I’m trying to determine how many years it will take to pay for the upgrade.
BTW, this just concerns the foam because regardless there will be a new Tyvek wrap installed.
Replies
Just one of many web sites which offer heat loss software is: http://www.slantfin.com/heat-loss-software.html
What type of siding is currently on the house and what's going to happen to it when you reside?
One question about adding exterior foam insulation: if you're going to pay someone to fur out the framing and install foam insulation, why not go for 2" XPS instead of 1/2"?
Edited 7/10/2008 3:54 pm by Hudson Valley Carpenter
I'd not do it, for the few R you get. Airsealing pays higher returns IMO.
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations
You gonna play that thing?
http://www.youtube.com/watch?v=32Ln-SpJsy0
Hard to say how long before the upgrade will pay for itself. Eventually it will, if not for you, but for a future HO. For simplicity sake, assume your monthly utility bills are ~$200 ($2,400/yr), and the upgraded foam walls save you 25% (a reasonable guess), it will take you >7 yrs to recoup your costs. Sealing your attic will probably pay back sooner, but adding foam in the walls isn't a bad idea.
FHB recently had an article on insulation upgrades with cost/benefit discussion. Worth a read.
I foamed my house this winter. 1" extruded polystyrene. Made a big difference that was immediately noticeable. You don't say what kind of house you have. Mine was an old house with board sheathing, degraded building paper, and blown in cellulose, so I think wind wash was costing me a lot of R value. My highest gas bill used to be about $280. After the foam, it was about $200. That doesn't factor in the price of gas and the degree days. Also remember that the payoff period is affected by future prices. The real payoff to me was in comfort level on cold days. I used to know it was a cold morning without even looking at the thermometer. Not anymore.
That's my house. I think a lot of the value of foam is blocking wind wash and preventing thermal bridging. Where you already have 1/2", the additional foam is not going to have as big a payoff, I think.
Not sure I agree with him on the one inch of foam. He has to find the studs anyway. Hardie can be nailed through 1" of foam. Why does it change when he's going from 1/2" to 1"?
That price seems high to me. I just installed 2" foam and 1x2 furring strips on an addition that I'm building and it only added up to about $1.50 per square foot with labor. It sounds like you have a little over 2,000 sq. ft. of wall area(assuming your house is mostly a box), which should be closer to $3,000. The 1/2" foam is much cheaper that the 2". You shouldn't even bother with it if he's going to install the 1x2's over the existing foam and friction fit between with the new. One of benefits you get from foam is that it will air seal the wall envelope and have a continuous R-value, and that would be greatly reduced if the foam was only installed between stud bays. He should foam the whole thing and tape the seams, and then fasten the 1x2's on top of it. He'll have to use 3" screws(I had to use 5" timberlocks because of the 2"), to fasten them, and then nail the siding to the strips.
If you can't get the price down a great deal, I'd skip it and air-seal the attic and crawl only. That is something that will pay itself back very quickly.