HOW VENTILATE AND INSULATE A LOW PITCH HIP ROOF
QUESTION FROM TRICIA FROM FALMOUTH, MAINE :
Great website! What is the best way to insulate and more importantly, ventilate an addition with a hip roof and a very low pitch?
ANSWER TO QUESTION:
The rafters are 2x8's. The roof overall is 26'x8' and the max height where it meets up with the house is maybe 2'-2 1/2' high.
Originally, we insulated with the pink fluffy stuff. R49. Above the rafters. We developed a serious condensation issue which many have attributed to lack of ventilation since the insulation was pushed right up against the sheathing for at least ½ of the roof – front to back.
We pulled out the insulation, let it dry and now are thinking to put in a power vent type item against the sheathing, and then replace the Pink fluffy insulation, but perhaps not so thick along the perimeter where there is really just no height.
Some have suggested ditching the insulation and spray insulating the inside surface of the sheathing and rafters – but that is pricey and we have already bought the pink stuff so would like to use it. Thank you!!
ANSWER FROM THE INSULATION DOCTOR:
I would need to know if you are planning on insulating the underside of the roof line or do you have a flat ceiling below the roof line?
If you are planning on insulating the underside of the roof line I will need to know the dimension of the rafters (for example, 2x8s, 2x10s, 2x12s??).
Please write back and let me know. Also thank you for the compliment on the website. We just finished updating it so it can be viewed on cell phones and tablets as well as PCs. Older websites do not show up well on the newer mobile devices. My wife does all the website work.
The Insulation Doctor
Regarding insulating the ceiling, it sounds like you have made the proper adjustments with one exception, which is you are not getting enough air at the lower end of the attic in the space between the top of the insulation and the underside of the roof.
What you need to do is purchase from your neighborhood box store, like Lowes or Home Depot, an item referred to as a Baffle, commonly called a Proper Vent. This is a styrofoam shoot that you staple to the underside of the roof deck stopping the insulation from compressing against the underside of the roof and creating a 1-1/2" airspace for 4' to 8' long. I would recommend that you install them the full length from the lowest part of the attic to where there is an adequate air space existing. This may encompass 12' or 16' in each rafter space.
The key to this is to have installed soffit vents on the outside underside of the overhang. This will allow the air to come into the attic and travel up the underside of the roof deck and be exhausted by your power vent at the top of the roof. If you do not have an overhang there are 4" round screened vents that you can install on the fascia board of the exterior.
If you have any questions please do not hesitate to email me again. Hope this helps.
The Insulation Doctor