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Sticking With Spray Foam for My Renovation

I wanted to try a different type of insulation, but it just didn’t make sense to switch horses in midstream

Posted on Dec 10 2013 by Carl Seville, GBA Advisor

Over the past dozen or so years my opinion on spray foam insulation has evolved from being a strong advocate to being slightly skeptical.

I have come to the conclusion that any well-designed new building can be insulated with any properly installed insulation. When it comes to renovations, however, spray foam often has some distinct advantages.

About eight years ago, I installed spray foam on the roofline and floor of my house, which, I now realize, was not a particularly good decision. Since I had no HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. ducts in the attic, I probably should have insulated and air sealed the ceiling, and sealing and insulating the crawlspace would have been a better choice as well.

But that is all water under the bridge. I would have preferred to use something else in my current renovation, but since the floor and roofline were already insulated with spray foam, it didn’t make sense to switch products (and relocate the thermal enclosure location in the process).

What should I do with the walls?

Ready for insulation, I hired an experienced Icynene installer to insulate the new walls, roofline, and floor areas, as well as to touch up some thin areas from the earlier install.

I chose not to install any insulation on most of the existing exterior walls as they were not being stripped. The existing wood lap siding is in excellent condition, and with no sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. or weather barrier, I was concerned that installing insulation would lead to moisture retention in the wall cavity and possible damage to the structure and siding. Since the climate in North Georgia (Zone 3A) is relatively mild, I decided that the added value from wall insulation would not be worth the risk of moisture damage, and removing either the siding or the plaster to allow the walls to be insulated was not in the budget.

At the one small section of wall where the interior was exposed, I installed felt on the inside of the wall to keep the insulation away from the siding, providing a sort of makeshift rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. between the siding and the insulation. I can’t say for sure how well this will work, but there is enough of a roof overhang that any moisture that gets in the wall cavity should be able to dry out, keeping the wall safe from damage.

Rolling towards completion

Insulation and drywall are installed, interior finishes are moving along smoothly, and the house should be ready to re-occupy close to the end of the year. The outside work is progressing, although some bad weather and the Thanksgiving holiday slowed progress a bit.

I’m looking forward to seeing how well the Home Slicker rainscreen works with the siding – a combination of reused and new material. And I am particularly interested in seeing the Perennial wood porch flooring and rails installed.


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  1. Carl Seville

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