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Ask the Architect

Installing shingles in wet weather

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Q. Lately, now that it’s spring, I’m seeing roofers putting on new shingles and assume people are getting leaks that must be making them a little desperate, because roofers are working on wet roofs or in cold weather or when it’s drizzling. Can roof shingles be put on in wet weather? I was taught by my father, a carpenter who was extremely careful with everything he did. I learned what to do (and not to do) from him, and he never would have allowed this. Is there something about today’s products that allows them to be put on in wet or cold weather that I don’t know about?

A. Shingles aren’t the only things being “put on.” Wet weather and construction don’t mix. Homeowners are being misled by people they hired to do the right job.

One of the first lessons in architecture is the detailed understanding of how water and movement affect buildings. Your observation is correct that installing materials in wet conditions should generally be avoided. In the case of putting shingles over shingles, there’s an assumption that the heat of a hot, sunny day will dry everything out eventually, but the slowly developing damage has already begun, hidden from sight.

It’s generally not the first thing people think of, but the world we live in exists in multiple levels of scale, from nanoparticles to cells to larger molecules and visible materials. In other words, seeing may be believing, but what you can’t see is still there, and what you can’t see happening is still happening. If we only think of water as big droplets, forgetting about gas (vapor) and solid (expanding ice), or that many materials allow water vapor to squeeze between their molecular structures, then it will be harder to understand the level of permeability or penetration of a material, like the wood sheathing below the shingles — or that a thousand nails were just driven through the vapor barrier sheeting below the shingles.

For installers, it becomes a gamble, a game of risk, to someone else’s cherished property through a bunch of assumptions: that water won’t get through, or won’t be locked in, heated by the sun, forced by pressure like a thousand little boiling tea kettles to push moisture around the nails and into the wood sheathing, or to cause the semi-rigid shingles to be forced by expanding frost to keep flexing and contracting, shortening their useful lifespan of protecting the inside of the house. Once this occurs, the materials have made accommodation for vapor and have slightly expanded, but after expanding, they don’t immediately contract again. They now have a much greater flexibility, and all because the moisture crowbarred its way in.

I often wonder if those installers would leave their windows down in a car wash. They have little to lose, because if the shingles fail prematurely, they’ll be back sooner.

© 2020 Monte Leeper. Readers are encouraged to send questions to yourhousedr@aol.com, with “Herald question”  in the subject line, or to Herald Homes, 2 Endo Blvd., Garden City, NY 11530, Attn: Monte Leeper,  architect.