Product performance on KLEER used in exterior trim
L@B_376
| Posted in Green Products and Materials on
I moved into my new home last April and have notice that the material called KLEER lumber used on the eve facia shrinks at cold temps – a lot. Factory rep inspected it at 33 degrees. I have photos at 15 degrees with joints open enough to see the framing material under the trim. Does it continue to shrink as temps go down? Is this a material that was not intended for exterior use?
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Replies
Lois,
Kleer is made of cellular PVC (vinyl), and cellular PVC has a high coefficient of thermal expansion. That means that it expands and contracts with changes in temperature.
There are ways to disguise this expansion and contraction, and your builder should have been aware of this fact and should have employed the tricks that builders use to disguise these changes.
Many years ago, I wrote an article on this topic for the Journal of Light Construction. Here is a link: Engineered Exterior Trim.
In that article, I wrote, "Unlike engineered wood trims, which expand and contract with changes in humidity, plastic trims expand and contract with changes in temperature. In the case of cellular PVC, for instance, a 55 deg. F increase in temperature will cause an 18-foot piece of trim to expand in length by about 3/8 inch. 'It is important to remember that this stuff shrinks in cold temperatures,' says Steve Roth, director of marketing at Style-Mark, a manufacturer of polyurethane trim. 'That's why you need to spring-fit the butt joints, and always use adhesive. Otherwise there will be a gap when it shrinks.' Thermal movement in fascias can be disguised somewhat by the use of scarf joints."
Lois,
It's worth remembering that PVC doesn't so much shrink at low temperatures as expand or shrink depending on how warm it is. Unless installed at the hottest temperature it is likely to experience, it needs to be installed with a gap, or it is as likely to bulge or buckle when it heats up as it is to shrink in the cold. As Martin said, builders need to take this movement into account when installing PVC trim.