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Replacing siding (and TenTest or not?)

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Posted by: from Angus
5/11/2011 at 11:59:21 AM

I have a 30 year-old home with vertical shiplap wood siding. The old siding is cupping, cracking, etc so I want it replaced. The old siding nailed directly over 5/8" TenTest (basically thick black tar impregnated paper). The TenTest is nailed to the 2x4 wall studs. I want to use a prefinished wood or composite siding to replace the old siding and at the same time, I want to add insulation and make the walls more airtight. I can see various options:

1. take off the old siding, wrap the house in typar and install the new siding;

2. take off the old siding, install 1.5" or so of panel insulation (eg, Firestone Polyiso) and install new siding;

3. take off the old siding, take off the TenTest, check/renew the insulation batts between the studs, install OSB, install 1.5" panel insulation, install siding.

So the advice I'm seeking is as follows:

1. How far should I go - should I take off the TenTest or not? What approach would provide the best value for dollar spent?

2. Recommendations on wood siding products - I'm thinking of something like Gemthane but there are others such as Hardie boards (one company told me they don't use Hardie composite products because of carcinogenic risks). From your experience, what is the best wood/composite product?

3. One estimator suggested siding directly over the existing siding - is this a good idea?

4. Any other thoughts, recommendations, etc?

Thanks and regards

REPLIES (3)
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Dave in Oshawa
Date/Time5/11/2011 at 12:36:50 PM

Hi Randy,

You have several different things going on it seems. Ultimately, you need to decide what it is you're really after? If you want to make the outside look nice, you could simply invest in a really good paint job and replace only the boards that are cupping or cracked. If you want to go for the energy efficiency aspect, then obviously there is a lot you can do. The trick is going to be figuring out what your real target is otherwise you can blow your budget pretty quickly. My answers to your questions are as follows:

1) there is nothing wrong with ten test. Without getting into a whole building science debate, ten test has more admirable properties than many building products today. My motto is, if it ain't broke don't fix it! You won't know the real condition of the ten test until you start stripping off the old siding. If it is in decent shape, leave it alone. Where there are damaged areas, you can make repairs using OSB/plywood and roofing paper. But again - this all depends on what you're trying to acomplish?

2) Recommendations on wood or composite products - some others might be better able to jump in on their preference. I suggest if you're going the full replacement route, choose a product based on it's long-term durability and maintenance free qualities. I assume the only reason you're doing away with the existing wood siding is because it's been difficult to keep up with painting, etc.

3) Siding over the wood - you can do it, sure. There are plenty of examples of Victorian homes that have been wrecked by slapping aluminum or vinyl siding over the top of the preexisiting cladding. Again, I question what your motives are for covering the wood? An intensive paint job might work out to be less than residing with vinyl - but it will require on-going care.

4) In terms of energy efficiency, there is a ton of stuff that can be done if you're going to the trouble of stripping the exterior of the house. My caution in using some exterior styrofoam products is they *can* act as a vapour barrier. Check the manufacturer's specs to be sure. You want a product that "breathes" on the outside like tar paper, ten test or Typar/Tyvek. It's important to allow any trapped moisture in the walls to escape. And remember to install from the bottom up to the roof, overlapping joints 6"-8".

~ Dave

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Randy in Angus
Date/Time5/11/2011 at 5:28:19 PM

Dave, thanks for the reply. The existing siding is cupping in quite a few places so I'd have to replace quite a bit - 20% at least so my aim is to replace it with something that doesn't need much maintenance and while doing that, add some R value, seal up the envelope a bit. So the aim, the answer to your question, is both long term maintenance and insulation.

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Dave in Oshawa
Date/Time5/12/2011 at 9:39:19 AM

Hi again Randy,

In that case, I think to achieve your two primary goals of increasing R-value and air sealing, adding an exterior insulation product would be the simplest all-in-one solution. There's really no need to remove the tentest if you don't want to (again depending on condition. If there is water damage or mould or other nasties, of course take it off). You can apply the exterior insulation over top and then new cladding over that. The exterior insulation will provide a good air-barrier if sealed properly. The trouble you're going to have is extending your door/window jambs and sills the extra 1-2" to make them weather tight. It can be done, but it's fiddly work. Good luck with it!

~ Dave

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