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Community and Q&A

Layering up siding on an old house

dnardoza | Posted in General Questions on

I have a house build in 1868, I have been doing an enormous amount of work on it since I bought it about 7 years ago. The house has the original clapboard siding covered over with asbestos siding which was done a long time ago and is looking very dated. I realize tearing off the asbestos, praying the wood underneath is in good shape and bring back the house to it’s original state would be great, but that would be very expensive and would insure a whole lot of work in the future to keep it painted if not work a lot of money. Also there are 3 dormers and a (what I would call a knee wall) around the wrap around porch that are the original shake, and they are looking pretty beat up. They need repair and painting, as well as the asbestos siding is looking weathered.

Long story short we decided to go with vinyl siding. Cedar Impressions on the dormers, the porch knee wall and the 4 gable peaks of the house, followed by 2 rows of scallops and then the foe clapboard vinyl siding that is most common. I thought it was a good idea to get the foam backed siding on the house for 2 reasons, I was thinking it would look better and the extra 4 to 5 r value would be worth it. The siding guy says the foam breaths and prevents rot … ?

Again it’s a very old house, I do a lot of work on it myself I have had to open up a bunch of walls for a bunch of reasons and I have either found no insulation or shrunken foam that was blown in many years ago and has obviously shrunken to worthless proportions. So I have realized that at some point I am going to have to open up every exterior wall and insulate but in the meantime and even after the insulating factor of the foam siding should help right?

All of the siding guys suggest we go over the asbestos siding (although they would take it down for a price) it seemed like a good idea to me to leave it up, one more layer on the outside of an old house should help keep the house a little more insulated. But then I started to wonder and went to the internet to get answers.

I found this site a few days ago and have been reading a lot, by the way this site does an amazing job bringing a lot of information to people. Great Job! With that said I learned a lot which is to say the more I read the more I realized there is so much I don’t know. Things like moisture and rot and barriers ugg.

So now I don’t know if I am making a huge mistake, I don’t want a rotting house on my hands. Any ideas, thoughts suggestions, I have no idea what is the best course of action.

And yes I do realize vinyl siding can look very cheap , but I have seen it done to look more like an old house and less like a plastic box when done right, and the idea of power washing once in a while as opposed to painting 3 stories of house is a big draw. Thanks for any input I can get.

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  1. user-659915 | | #1

    If as you say the main reason for covering the asbestos is that it looks 'dated' I doubt you'll be happy with the look of the vinyl either, at least not for very long. And (who'd have thought a vinyl siding salesman would ever mislead a potential customer) the insulation will be practically worthless.

    Obviously the dormer siding needs to be replaced ('d recommend a cement board faux shake product over vinyl any day) but why not save the money you'd spend on covering the asbestos with an even crappier product and spend it instead on proper insulation and airsealing of for the most critical parts of the house. Start with tops and bottoms - attic and basement - for maximum bang for the buck. To a man with a hammer everything looks like a nail. You need to talk to a reputable and experienced builder, not a siding salesman.

  2. GBA Editor
    Martin Holladay | | #2

    Here's another vote for keeping the asbestos siding. Asbestos siding is much better than vinyl, and yours looks to be in good shape. Asbestos siding holds paint amazingly well -- three times longer than wood siding, I'd estimate.

    There are no health problems associated with asbestos siding, as long as it remains on your house and is not disturbed by someone like a vinyl siding installer.

  3. Expert Member
    Dana Dorsett | | #3

    Fiber cement siding over a 1/4" or 3/8" fan-fold XPS underlayment detailed as an air barrier will do more for protecting the dormers from moisture than foam-loaded vinyl.

    I've seen asbestos siding still holding paint well 40+ years after the fact. If you're still going to side over it you'll get more thermal & moisture benefit out of a layer of rigid foam detailed as an air barrier (or a continuous inch of closed cell spray polyurethane) than any foam-loaded vinyl siding.

    But before doing anything there it's worth figuring out what the old cavity foam is, and how to insulate over/around it. Modern foams don't have severe shrinkage issues- I'm not sure how well the urea formaldhyde stuff from the 1970s holds up under different climates but I've seen some still in pretty good shape in a US zone-4 temperate climate location. I may have shrunk to those proportions the day after it was blown due to improper mixing or improper temperatures, rather than over decades(?). After decades of outgassing it's probably not a measurable health problem worthy of removal, but it has shrunk to the point of pulling away from the studs & sheathing it's not doing a whole lot for you, and insulating around it may be difficult/awkward. If you are eventually going to be ripping it out from the exterior side it's cheaper & better to deal with it BEFORE residing (or even re-painting.)

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