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Looking for the best route (complete the condition attic or fix the venting issues)

anthocruz | Posted in GBA Pro Help on

In a 1979 home in the Houston area. They installed open cell foam on the rafters without removing the blown insulation.
Issues:
1- They installed open cell foam (3in -4.5in) on the rafters without removing the blown insulation. Because of that the top plates were not seal. This allows air to still migrate from the soffits available. However the ridge vent is sealed. 

2- They left the same furnace and type of water heater. Some of the foam  around it looks like it has slowly burned.  Having different color. Will have to remove that section of the foam do to possible  chemicals residues

3- I am able to remove the foam to easy on areas that appeared to have water damage. Concern about the whole installation.

What I have done:
1- Already remove the blown insulation and sealed all penetrations in ceiling

2-Replace the water heater with a high efficiency tankless

3- Took exhaust vents and vent pipes thru the roof

What I am debating.
Once I Remove about 2 -4 ft of spray foam from the edge and the damage sections from the ridge
 Either
-Seal the top plates and get someone to spray those areas, along with any other section I removed (if this then I will add vent in the attic). Then replace, the furnace when possible 

or
– Finish removing foam from the ridge, add  more soffits and add blown in to make it a vented attic.

Thanks for the help.

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Replies

  1. user-2310254 | | #1

    I'll give your post a bump and add a couple of comments.

    Leaving the blown insulation on the attic floor isn't a problem unless its compromised. But if the combustion appliances were vented into the attic, that is crazy and makes me wonder what else might be wrong in the house. You probably should get a competent inspector to go over the home from top to bottom.

    A vented attic reduces (maybe overrides) the effectiveness of putting spray foam on the sheathing. It also increases the risk that the sheathing will rot (especially in your climate). See https://www.greenbuildingadvisor.com/article/open-cell-spray-foam-and-damp-roof-sheathing for more information. Three to 4 inches of open cell is not sufficient.

    Keeping combustion appliances in an attic with spray foam sounds risky as well. In my townhouse, I installed spray foam on the roof sheathing, but I also converted the appliances to electric. It sounds like there is no combustion barrier between the foam and the appliances in your attic. With those appliances, where are they getting the air to burn fuel?

    When you installed the tankless water heater, did you relocate it out of the attic?

    You need to decide whether you want a vented or condition attic. If you decide on the latter, I would close off the eave vents, thicken up the foam, and get rid of the combustion appliances.

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