Your program will perform wonderful, provided that the layer of rigid foam in addition to your roof sheathing has an R-worth of not less than R-twenty. When you are working with XPS, you need at the least four inches of froth. In case you are using polyisocyanurate, you would like not less than 3 inches of froth.
The principle flaw During this roof looks to be the ice and drinking water membrane at the best stage inside the rafter bays. Would just standard felt paper have authorized enough humidity to dissipate from the roof sheathing avoiding rot?, I kind of question it.
If you choose to install open up-mobile spray foam in lieu of shut-cell spray foam, your roof assembly will be able to dry somewhat to the interior. Just Ensure that the spray foam layer is thick ample to keep the rafter bays higher than the dew level in the course of the Wintertime.
Yesterday we blew the insulation and mounted the SIGA Majcoat around the CAPACES Leadership Institute. There was over eight,000 Cubic toes of insulation to setup, so our insulators had 2 in their blower vans and a great crew on web site. They were being blowing cellulose as fast as they might along with the the rain was heading our direction. Lower than forty five minutes once the insulation was concluded we had finished the Majcoat and were hectic taping seams.
I have created log homes while in the Yukon Territory in northern Canada for thirty a long time. Most log buildings have cathedral ceilings. Most of the roofs We've built are as follows (from the bottom up): log purloins, nominal two" (2x6) t&g decking, 6mil poly, 1 1/two" extruded polystyrene foam, 2x10 rafters on 24" centers, seven" fiberglass, 2x4 strapping, 7/16 OSB, underlayment (15 lb paper, 30lb felt, or now we'd even use ice and h2o defend). There could be about an inch of air space underneath the strapping for the two vertical and horizontal air stream. All roofs are vented with strip vents within the eaves and vents inside the soffit (2x6 t&g) at the height at equally ends. I might disagree that venting will not be desired for those who stop the airflow on The nice and cozy side, for 2 good reasons. First it is actually very difficult to prevent all airflow, Primarily with conventional common methods (ie chimney and plumbing vent penetrations with the roof) We have a number of techniques created over time to seal the vb within the eaves and gables, but there are still nail penetrations throughout the vb. General I think we had incredibly tight seals but just one could never ever say airtight.
If it looks as if I'm outside of published here my depth listed here... yeah, you bet, I'm. I am only a homeowner, with only some days of Online research beneath my belt. But the contractor will not be knowledgeable about this roofing system, so we're being forced to figure it out jointly. Take pleasure in your enable immensely.
Like Doug's structure, the focus is on creating a superior perm layer for drying to the look at these guys exterior, that should even now permit venting although blocking wind washing within the fluffy stuff.
Sure, it truly is Harmless (While before you decide to ask an issue about a particular roof assembly, It could be fantastic to grasp your weather zone).
My advice could be to seal the existing vents. If insulation contractors in your area are setting up 3 to four inches of shut-cell spray foam over the roof sheathing, there's no need to concern yourself with condensation or moisture accumulation as part of your sheathing.
Sorry, Martin, I now understand that "new building" will not always imply "new home being constructed", and "an unvented attic, with R-fifty beneath the roof" must have been "an unvented attic, with an R-fifty roof'. Just because It truly is obvious to me doesn't suggest it's distinct to Anyone else.
You are proposing an unusual technique of insulating your roof. If I understand you correctly, you intend to set up EPS involving the tops within your roof trusses plus your roof sheathing.
Does it make sense to spray and Lower and cobble four inch shut cell foam/board on underside of sheathing followed by fiberglass In the bays and one inch of eps/iso under the rafter (to prevent thermal bridging) before ending with drywall? Will I create a vapor sandwich and greater depart the ultimate EPS and take the thermal bridging?
I have constructed dense-packed unventilated roof assemblies various occasions without the need of issue. Obviously I have not torn into them either. I would want to see far more examples of failures in These types of assemblies should they're around.
Cellulose insulation can shop lots of humidity. This "dampness buffering" capacity is cited by some cellulose supporters as An important edge, and without a doubt this potential can from time to time prevent a little dampness difficulty from producing many rot.