Insulating Roof And To Vent Or Not To Vent

Morning Wood

I'm doing an addition. It's about 2400 sq. feet. It has double 2x4 walls 10" thick frame to frame. The walls are getting blown with dense pack cellulose. But the roof I haven't quite decided on yet. I can't decide if I should build it as a hot roof or a cold roof. And if I build it as a hot roof what type of insulation I should use. Another option I'm exploring is double sheathing the roof with 2x4's on the flat inbetween the sheathing layers and venting the roof that way. Both I and the homeowner are a bit worried about material costs with that method though. But I think it is probably a very good method if feasible. If I go with a hot roof, I have heard in the past that closed cell spray foam is the only option. But I have heard from different insulating contractors and worked on jobs where cellulose had been used and open cell foam as well. I could also spray 2-3 inches of the closed cell stuff and then finish with cellulose. I just want to do this roof the best it can be done, but without breaking the bank for the homeowner. Any suggestions or thoughts? Thanks, Nick.

SLSTech

To my knowledge - Closed cell is the only tested & code approved method. I prefer Demilic's system but definitely check on the installer. Closed cell is expensive - you could possibly go with what is called a splash & dash system - Closed cell sprayed first 1 layer = 2" the finish it off with open cell which is cheaper due to its expansion 1 layer = 4"? as I recall. I can't see using cellulose / other blown in insulation with closed cell unless you can guarantee that it fully fills the cavity.

FYI - your location would be helpful, along with the type of roof structure, is it all cutup, cathedral ceilings, rafters or trusses, etc... There are numerous options available but without more info - that's all anyone can really give you at the moment.

__________________
Alabama Full Service Remodeling, Renovation, and Preservation by SLS Construction
Certified Energy Efficiency Audits, Ratings, Modeling, Verifications, & Consulting
Residential, Commercial, & Industrial Infrared Thermography Scans

Morning Wood

I'm located on the North Shore of MA. about and hour north of Boston. Within 1/4 mile of the ocean. It's a mix with the roofs. Part is cathedral and part is just regular with collar ties. Also, there is a bunch of metal shed roofs on the first floor. I think I'm not going to vent those. The collar tied roof has to be insulated in the rafters because there is a solar collector on the roof and access inside the roof space has to be maintained.

SLSTech

Fun, fun - as you are looking for an insulation contractor - see what their options for you are. I would suggest a Demilic contractor for the closed cell portion. Some simply do the foam systems, but you may get lucky & find one that installs other types of insulation & know the pro's & cons. Make sure anyone that states that there systems are tested & code approved provide the documents. It is amazing how many of them can't, or simply never call you back.

__________________
Alabama Full Service Remodeling, Renovation, and Preservation by SLS Construction
Certified Energy Efficiency Audits, Ratings, Modeling, Verifications, & Consulting
Residential, Commercial, & Industrial Infrared Thermography Scans