Thermal distortion and your old house

By: Conrad Neuf , Contributing Writer
In: Old House Inspection, Old Houses, Old House Construction, Home Improvement Tips, Old House Musings, In The News

One of the things I’ve always liked about the construction industry is that no matter how long you’ve been in it, you can always learn something new. My lesson today was on thermal distortion. Most people know that vinyl siding can melt–and if they don’t, they soon find out when the grill gets too close to the siding on the rear patio. I wish I had a dollar for every time I’ve been in a homeowner’s rear yard and had them ask me why their siding was distorted in a particular area. It was usually obvious they had moved the grill and were hoping I’d fall for the old it’s-defective-siding ploy.

Thermal Distortion--photo from greenbuildingadvisor.com

Thermal Distortion--photo from greenbuildingadvisor.com

I was talking to a siding salesman today and evidently thermal distortion has turned into a big problem with vinyl-sided homes across the country. It seems to be of the same proportions as the problems we had with certain types of stucco a few years ago and roof sheathing back during the ’80s. Modern windows have become so good at reflecting the sun’s heat that they’re melting the siding on neighbors’ homes. It’s similar to the principle you demonstrated when you were in the Girl Scouts or Boy Scouts and used a mirror to burn clumps of grass.

Who’s to blame for thermal distortion?

One of the problems with the thermal distortion fiasco is that no one seems to be worthy of blame. Most vinyl siding is designed to resist deflection up to around 160-170 degrees, which has been fine in most situations. Window companies are doing their best to make their products more energy efficient and to provide homeowners with lower cooling costs. Unfortunately, when the two products are put in close proximity thermal distortion can result.

Who's At Fault?--photo from greenbuildingadvisor.com


Most of the episodes reported seem to be occurring in newer communities where the homes have been built on top of each other. However, I can also see it becoming a problem in towns where old houses are close and owners are restoring their homes with vinyl siding and high efficiency windows. There’s no doubt in my mind that if my neighbors installed windows with upgraded Low-E coatings, the reflected heat from the summer sun would be enough to melt vinyl siding on my home. It will never be an issue, however, as my old house will always have wood siding.What’s the solution? The siding salesman told me his company had developed a siding panel capable of withstanding 220 degrees, but it must still be in the testing stage, as I don’t see it on their website. Other possible solutions include telling your neighbor with reflective-coated windows to keep screens on their windows or to plant shrubs between your homes.The lesson here is that if you’re thinking about putting vinyl siding on your old house or you see your neighbor installing new windows, keep thermal distortion in mind.


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  1. 8 Responses  to “Thermal distortion and your old house”

  2. Dec 2, 2014
    I replaced the whole side of my house with new vinyl siding because of thermal distortion. My neighbor windows reflect the problem. She refuses to make a solution. Is this a legal matter or are you able to suggest another modification we can do ? 2 months after replacing the siding it has only come back again.
  3. Dec 2, 2014
    Thank you for your educational article. I had this problem over the summer, I had no idea why, my neighbor said oh you washed the house. So I had a siding specialist come and replace the vinyl siding on the whole side of the house even though the damage was only 3/4 up.It is now 2 months later and it has already started. So now we need a solution which needs to involve our neighbor. We approached them and saw the "he she devil" instantly appear. We are going to show them this article and see if we can come to a amicable solution. She does not want screens and shrubery may not be the answer. Are people taking this to court. Do you have any suggestions of any additional things we might be able to do. Desperate for an answer, thank you... John Fugett 908 - 272 - 8864
  4. Aug 29, 2011
    Hi Iris, Most of the heat generated from the sun passes through regular windows--my dogs are very appreciative that I have normal glass in my windows. They have their spots picked out to catch the afternoon sun. The windows have to have a reflective coating on the surface of the glass for thermal distortion to occurr. Conrad
  5. Iris
    Aug 29, 2011
    Is this just a problem from low-e windows or does reflected sunlight from regular windows cause vinyl siding to melt, too?
  6. Aug 29, 2011
    Yeah - sticking vinyl on an old home is NOT "restoring". Poor choice of words.
  7. Aug 29, 2011
    Hi Joe, That's a very valid point and I actually thought about that as I typed that word last night. I guess it all depends on someone's definition of "restore"and whether they want the future upkeep of wood siding. I'm in your camp as I think if an old house had wood siding it should remain that way. That being said, I see a lot of old houses being "restored" in my area with vinyl siding and I'm a little envious that their days of working on a 40 foot ladder with a paint brush in 90 degree heat are a thing of the past. Conrad
  8. frank
    Aug 29, 2011
    Vinyl siding has always had issues, but the industry doesn't talk about them much. Did anyone ever see the documentary called "vinyl is final"? It's worth watching and delves into the problems with manufacturing and disposing of PVC..
  9. Joe
    Aug 29, 2011
    Conrad, great article with one minor change required. Ok, take the sarcasm in jest... "owners are restoring their homes with vinyl siding and high efficiency windows" seriously? Restoring their homes with vinyl? come on.. not from oldhouseweb.com. How did this get past the editor? Ok, sarcasm over.. point made ? Joe