Roof ventilation expert recommendation

[newstove]

Hi. I'm looking for recommendations for an expert (or a "very good" at least) company/person who deals a lot with roof ventilation in the Central Massachusetts area. Now, I could pick anyone who does roofing, but I've run across too many hacks, so I figured I would look for recommendations first.

I had some isolated ice dam problems this winter, and the first thing I want to do is make sure that I have adequate roofing ventilation. I've run the numbers, and it may or may not be good enough, so I want it checked out personally.

The next step will be to start dealing with other problems (such as insulation, radiant barriers under the rafters, etc.) but the first step is to make sure the ventilation is up to par. I do have soffit/ridge vents in all affected areas, but I want them checked out and looked at for the potential for enlargement if necessary.

Thanks in advance for any advice/recommendations!

 

[Jack Straw]

I know around here companies offer energy audits. They come in and run several different tests on your house to show where you are loosing heat. This maybe a good place to start if they aren't too expensive.

 

[newstove]

Thanks, I had thought of that. I'm not so worried about losing heat as I am that the roof gets enough ventilation.

I have an air exchanger in the attic (I blame the builder for that faux-pas) but I'm stuck with it now.

So, what I want to do is make sure I have enough ventilation in the attic so that there is good air flow.

Then, I will be taking various steps to ensure that the air handler is not leaking heated air into the attic, and also that it is as insulated as possible.

Of course, no matter what I do, the air handler in the attic is going to give off some heat at some point - just the nature of the beast. So, I plan on also then applying radiant heat barriers at the underside of the rafters, and that is where the attic ventilation becomes key - I need to ensure that the soffits and ridge vent will properly flow enough air. There will be small gaps at the top and bottom of the radiant barrier for extra air flow.

This should in the end keep almost all the heat away from the bottom of the roof decking, while still having airflow moving upwards between the roof decking and the radiant barrier, and then out the gaps at the top and out the ridge vent. The warm air underneath will flow up the inside of the radiant barrier and out the ridge vent as well.

This is supposed to help me both in the summer and the winter (summer keeps the attic cooler, winter keeps the roof decking cooler because the radiant heat never reaches it.)

We shall see...

Thanks!

 

[DAKSY]

Hey, Newstove...

Try here:

http://www.askthebuilder.com/B335_Calculating_Ventilation_Area_of_Attic.shtml

 

[newstove]

Thanks. I've done similar calculations before.

So, let's see. According to that calculation, I need ventilation for 1064 square feet (38x28) and using the 1:300 ratio he gives, that makes it 3.54 square feet needed of ventilation.

I have a continuous ridge vent. Being generous, we'll say 12 square inches per foot (he assumes 18"), and 38 feet long. That is 3.16 square feet. So, I would only need 0.38 square feet of soffit (not exactly realistic. ;-) ) I actually also have continuous soffit venting as well, but it's not plain screen, it's that metal stuff with ridges and screen underneath, about 2" wide. I'll be conservative and say that it only provides a maximum of 4 square inches per foot (they have paint on them, but look reasonably clear, blah, blah, blah.) That gives me 2.11 of soffit venting.

I have a total of 5.27 square feet of venting in that attic using some conservative numbers. Seems way more than adequate according to his calculations... Of course, it may be that I should increase the size of the soffit vents - he recommends larger soffit vents than ridge vent.

 

[Reggie Dunlap]

I build houses here in Vermont where we get a lot of snow and I've fixed a lot of ice dam problems. On new construction we are not venting most roofs. We use expanding spray foam on sloped ceilings and blown in cellulose on flat ceilings. The key to avoiding ice dams is insulation, not ventilation. More venting may help hide the symptoms of an under-insulated house, but more insulation will fix the problem and lower your heat bills.

If you have flat ceilings the most cost effective retrofit is blown in cellulose, it's cheap, effective, and easy to do yourself. It can be blown in on top of existing fiberglass. Just a few inches will seal up the gaps which is what is causing the air leakage. You'll need to build a plywood surround around the air handler and the access hole, if there is one.

The other option is to install expanding foam on the underside of the roof sheathing. This will be considerably more expensive but will work well.

Hope this helps.