How To – Exterior Insulation Considerations & Methods

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    In the past few years there has been a movement in the remodeling industry to add insulation to the exterior of buildings when new siding is being applied. Here we will look at the advantage of this process and drawbacks that come with it. It is important to weigh the good and the bad when implementing any new technology.

    The process is relatively simple as far as the installation of the foam board insulation goes.

    First the exterior of the home is inspected for any rot or wood damage in the existing siding. If vinyl siding has already been applied then it must be removed and the sheathing behind it should be inspected and repaired if necessary.

    After any repairs have been made to the structure you will want to make sure that all cracks and holes have been filled with caulk or spray foam insulation to reduce any transfer of air and loss of heat.

    A vapor barrier should be used and a Tyvek material is suggested for this application.

    Foam board insulation comes in a a variety of thicknesses but for this process you will use 2 inch thick 4×8 foot sheets which are nailed to the building with at least 3 inch long nails that have head cap backers to secure the material securely every foot on center. Construction adhesive can also be used but must not be relied on as the only mechanical attaching method.

    The bad part
    When installing insulation around windows, doors and other items you will need to extend jams or make allowances. This can be a difficult process especially if your windows have a flashing molding to accept vinyl siding.  You may end up pulling all of your windows and nailing on 2x material to build out the window. This will also cause problems inside the home where sills and drywall details will need to be reset.

    Once the foam is installed properly you should make sure that all seams are taped.

    Installing your Siding
    Because foam insulation is very unforgiving to water vapor it is important that you use vinyl siding over any exterior foam insulation.

    Wood siding will have a tendency to swell and cup at a higher then normal rate. The suns heat will also reduce the life of any wood product.

    If you do not like vinyl you might be better off with a stucco or cerement board product. Stucco is often used over foam insulation in commercial settings and new techniques can provide some very decorative effects.

    Vinyl must be attached with extremely long nails to secure correctly. You will find that penetration of 3/4 to 1-1/2 inches into the wood sheathing below the foam is necessary and you will want to hit every stud that you can.

    Drawbacks of this Method
    Well we have already seen some of the drawbacks due to windows and doors that will need reworking. This can be an expensive process and refitting these items is probably not worth it if you are not upgrading to better product.

    The attachment method of siding also removes wood siding from your selection. If you are fine with this you will still have the problem of using extra long fasteners to secure your vinyl. This will increase labor time and cost.

    Insects also seem to like to live in the foam. There have been reports that carpenter ants and other pests will make homes in the soft material and since it is not treated with insecticide once they get in there is really no stopping them.

    Finally the improvement of insulation factors for this method are very limited. Foam insulation is better then nothing but the material cost in addition to labor will not provide a final quality of living that you may be happy with.

    If you are replacing siding on a very old home you may see some limited improvement but foam insulation does not provide a high enough r-value in the thickness that is used to make this method of insulation worth while for most home owners.

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