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When ICF and SIP won't work

Last Post 08 Sep 2008 03:29 PM by Boontucky-girl. 24 Replies.

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Boontucky-girl User is Offline

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Posts:250

04 Sep 2008 01:32 PM
About the 2" of EPS, hardie siding only allows a max of 1" foam. That seems to be a problem, and it requires that you penetrate 1 1/2" of wood with the nails, so that's another problem. Certainteed does allow the use of screws that need only 3/5" of wood penetration, and doesn't limit the amount of foam and the furring strips would meet that requirement. I'd have to use 4 inch nails to secure the strips to the wall first. But I'll have to find who supplies certainteed around here and compare price with hardie. Is Owens Corning FormulaR the same as the DOW Styrofoam? I can't find anyone who carries 2" DOW stuff, but I saw that Home Depot has the 2" FormulaR. Thanks for all your help! Boontucky

Alton

Veteran Member

Posts:2157

04 Sep 2008 03:01 PM
In my opinion, if you use extruded polystyrene or insulation boards with aluminum foil such as Thermax and then tape the seams, then I see no reason to use a house wrap since air will not penetrate the insulation boards and OSB. House wrap or taping the seams should be enough to keep the rain from entering the wall cavity, especially if you use a positive drainage plane (void) between the siding and the insulation board. For new construction, I would use windows with nailing flanges. Again, IMHO, I think the flanges of the window should be attached to furring strips that line the opening. Then tape should be appled over the flanges according to a method that leads water away from the window. Hardie Siding is then butted up against the window trim and corner style boards. Wider furring strips around the windows will be needed in order to support the exterior trim. This means that the window trim will terminate the Hardie Siding. By the way, try to avoid using wood for corner styling, window and door trim. I prefer cellular PVC. Cellular PVC paints well and will hold the paint longer than wood. (Be sure to clean the PVC before painting.) I believe Hardie has corner style boards available if you do not want to use cellular PVC. If anyone sees anything wrong with the above ideas, please speak up now before someone relies upon my non-existent experience with weather in cold climates.

Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period . 334 826-3979

Boontucky-girl User is Offline

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Posts:250

05 Sep 2008 08:55 AM
How do you attach the furring strips to the wall? With long nails? Are there nails long enough for guns? Or do you have to pound them in one by one? How about screws? Hardie installation doesn't say anything about using screws, and for nails it says it requires 1.5" of wood penetration. That would mean I'd have to fur with 2x material, lest they void the warranty. Any thoughts?

Alton

Veteran Member

Posts:2157

05 Sep 2008 04:50 PM
Long screws would be the best way to attach the furring strips to studs through the 2" thick polystyrene. Then attaching the Hardie Siding to the 1 1/2" furing strips would be normal again. If you have to use 1 1/2" furring strips to meet Hardie's warranty, then it might be time to reconsider how to build. I am saying this because basically the wall is using too much wood and is getting too thick. A staggered stud wall built on a 2x6 base plate with spray foam in and around each stud should work well. Continuous OSB could be used on the outside of the studs to beef up the wind bracing. This type of wall would not contain a drainage plane nor the 2" of polystyrene. You may not need a drainage plane with Hardie Siding but a house wrap should be considered to protect the OSB. How soon do you plan to build? Look at other systems on the market. What else is available in your area? Alton C. Keown alton at auburn dot edu

Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period . 334 826-3979

Boontucky-girl User is Offline

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Posts:250

08 Sep 2008 03:29 PM
Thanks Alton, Yes, using 2x material is not an option. I am looking at certainteed fiber cement because they only need 3/4" wood penetration if using screws, so 1x material will be fine. It's a matter of finding a local supplier for a decent price. We actually started our building project today, officially. The excavator is currently digging our basement, and footings are scheduled to be poured this week or next week depending on weather. Also, we thoroughly compared the cost of ICF, SIP, and stick build and unfortunately, ICF and SIP will not work because the quotes that we received were almost 40% over our budget. We can make stick frame fit the budget, even with quotes for spray foam and exterior sheathing figured in. Right now we are going with 1" R-board, but I want to increase that to 2" if I can make the siding work. I am running out of time though, since we need to have the new basement dimensions before the footings are poured. We'll see how it goes.