Felt paper under vinyl siding

Q: I read with interest the article Vinyl Siding Done Right. The thing that caught my eye was the use of felt paper. I didn’t think its use would be recommended because, being black, it would absorb more heat. Isn’t there a chance that the felt paper would stick to the siding after being heated up, and wouldn’t that extra heat cause the vinyl siding to expand more?

A: Mike Guertin, a builder and contributing editor to Fine Homebuilding, replies: I shouldn’t be so critical, but this idea sounds like the start of an old wives’ tale. The Vinyl Siding Installation How-To Guide from the Vinyl Siding Institute (www.vinylsiding.org; 888-367-8741) and Vinyl Carpentry, the installation manual from Certainteed (800-233-8990; www.certainteed.com), both say that building paper, felt paper and housewrap all are acceptable, and that one of them must be installed over wall sheathing or studs before vinyl siding is installed.

Perhaps the caution about felt paper sticking to the siding is due to the notion that the black felt paper gets hot, which might liquefy the asphalt. That scenario is highly unlikely because the felt is not supersaturated with asphalt, only saturated. If the paper were supersaturated (a technical term I learned in chemistry), then the asphalt could liquefy and be released. Because it’s not, it won’t.

The other notion—that the felt would overheat the siding—would be the case only if the black felt paper were applied over the siding to absorb the sun’s heat directly. But because the vinyl siding covers the felt paper, it is shielded from the sun and never gets hotter than the temperature of the siding from solar gain. The short answer is that felt paper is fine as a weather-resistant barrier behind vinyl siding and will not cause a problem if the siding is installed correctly.