New metal shingle roofing question

Asked October 27, 2014, 9:00 PM EDT

I had new metal shingles put on two years ago (ranch style home) the underlayment was not replaced as the contractor felt it was in good condition. A few months prior to that I had 40 inches of insulation added to my attic (vent shoots were put in). Upon completion of my new roof it felt almost warmer in my house during the summer than before the insulation was put in. (My air conditioner is always on in the summer and to me it seemed the air conditioner would be running less in theory). I questioned the contractor about whether there was enough ventilation in my roof as to why it seemed warmer in my house. There is a ridge vent and some soffit openings for ventilation. I have charted my attic temps and it is consistently 30 to 40 degrees warmer than the ambient air in the summer time. This August I looked up in my attic and found that the plywood underlayment was coming apart in several places on my roof. My roof is therefore buckling and sagging in those areas which with metal shingles one would think that wasn't possible. I need to figure out why there was such a fast deteriation of this plywood when it was ok just 2 years ago. I purchased 40 year metal shingles thinking my roof with make it 40 years also but at this rate it will not make it but a few. My question is what is the attic temperature supposed to be for Iowa? My research on the internet comes up with a range of 15 to 20 degrees difference from ambient temps in general but is that the case for Iowa? Would the higher temps in my attic cause the plywood glue to let go and the plywood to "splinter" apart? How many holes in the soffit area does there need to be to provide adequate ventilation? Is a ridge vent adequate enough or should wirly birds be added? Is there a housing expert I can speak to or hire to give me advice? I feel that being a single woman that I am being taken advantage of and that no one is claiming responsibility for my roof problems and claiming they just don't know why my new roof has developed all these problems. I purchased what I was told would be a 40 year metal shingle roof. The contractor did come and used 2x4's to support those areas that were sagging and the plywood falling apart. To me this just puts a bandaid on the problem but doesn't fix the problem of why it started in the first place. Won't the problem just continue? I don't have the money to put on a new roof again. Any help would be greatly appreciated. Thank you for forwarding to whomever can possibly help me. I apologize as this is more than one question. Diane

Mitchell County Iowa home energy new home design and construction insulation and air sealing building construction

1 Response

Diane,

It's expected that your attic gets warmer in summer after adding insulation to the attic floor, since less of your air conditioning is cooling the attic. If your A/C compressor runs less now, that may be why it seems warmer inside but it may just really more humid or you have longer times when the cold A/C air isn't being supplied and blowing on you.

The roof decking failure is indeed a concern. Some possible causes could be that it's getting wet from either roof leakage or insufficient attic ventilation in winter. If there is no roof leak of rainwater, another possibility is a moisture vapor drive or diffusion through the underlayment that makes the decking swell and buckle inward. that indicates the plywood decking might not have been installed with adequate expansion gaps.

Sufficient attic ventilation is important in winter to prevent roof deck moisture problems. Ridge and soffit vents are typically rated for "clear vent area", and it's best if you have as much or more inlet (soffit) cva than ridge cva. Check with your local building code for how much ventilation is required by code.

I suggest you hire a licensed or ASHI certified Home Inspector who can inspect and use moisture meters on the roof decking to determine the root cause and suggest best solutions.

I'm so sorry about your ordeal!