Attic ventilation vs. radon
I am considering the purchase of a concrete block house built in 1960. it has a partial basement (not full). It is all-electric; electric 50 Gal water heater, baseboard heat–no furnace, no ducts, no A/C. The attic has zero ventilation (except for one 2.5 in. diameter hole from a woodpecker on one gable!). The soffits are solid wood–no ventilation holes at all. The inspector said the attic was pristine–no damage from woodpeckers, no nests, etc, and nearly a foot of blown-in insulation.
The roof on the house is three layers thick–cedar shakes on batt boards, then fiberglass shingles, then asphalt shingles. A few of the top layer are missing exposing the second layer. The existing detached garage also needs a full roof, but might not need a tear-off; it is also concrete block and is styled to look like the house. But the roof has gussetted trusses and plywood sheathing.
My offer will be based on sharing the cost of the new roof with the seller. I have requested a bid on a steel roof. This is in zone 6A and elevation is about 6000 feet. It’s in Central Utah, so weather is variable. The roofer making the bid has assured me that all his steel roofs have ridge vents. He will also include hole sawing the soffits to provide soffit vents to work with the ridge vent.
My question: I’ve read other posts about pressurizing the attic being a generally Bad Idea. However, this house in in a valley with nearby uranium mines. The inspector says radon is a real issue in the area. He says one way to reduce radon infiltration is to pressurize the house. Given there is no duct work, we have considered a window swamp cooler for summer cooling. We wonder about using a gable-mounted fan to blow air into the roof to keep a small amount of positive pressure in the roof relative to the house, purely as a mechanism for reducing radon infiltration. I understand that this could cause the house to be colder in winter or warmer in summer. I am not married to the idea, but would like some comments on whether there is any merit to the approach. If not, what alternative ideas could we consider?
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Try measuring the radon levels before spending anything on changing anything about the attic ventilation scheme. If the condition of the attic was pristine after 57 years of service there is no reason to ventilate it at the risk of pulling defeat from the jaws of victory there!
If the radon tests in double-digits pCi/L, deal with it via more conventional radon remediation methods, such as sealing the basement walls & slab, and depressurizing the slab. If there is crawl space under the rest of the house that doesn't have a vapor barrier, a heavy duty vapor barrier on the floor of that area is a good idea even if there isn't a radon issue.
If it's in single digits it's better just install HRV or other conventional active ventilation of the conditioned space, which has a greater spectrum of benefits than pressurizing the attic. If after ventilation it still tests at or above the EPA recommended 4pCi/L remediation point, bear in mind that the risk at that level is entirely theoretical, and even the theoretical risk low enough that most people have more important risks to worry about. (At 6000' the increased cosmic rays are a factor too- what's next, lead-covered concrete roofing? ) The EPA's radon limit is a recommendation, not a regulation, though ultra-high levels can affect how easy it is to re-sell the house.
When it comes to radon mitigation systems, I don't suggest experimentation. The conventional advice provided by radon mitigation experts is summarized in the following article: All About Radon.
Pressurize the attic and your house will smell like the attic.
This house sounds like an expensive repair job I would skip it personally