Q. "If I execute the unvented roof as designed and set 4 inches of polysio about the roof deck, am i able to then use open up-mobile foam between the rafters?"
I might drastically respect recommendations from experts: bite the bullet and hazard of spray foam insulation, or send out the builders back again up over the roof in December to chop ridge and soffit vents?
Till just lately, building codes necessary that insulated sloped roofs involve ventilation channels immediately beneath the roof sheathing. Lots of builders nevertheless observe this time-examined technique.
Rafters are 2x4, 12/twelve slope, and also the roof is difficult with intersecting ridge lines, valleys and dormers. (Your home initially had a cedar roof. The deck is the normal spaced fir planks.) Resulting from the development, there is nearly no potential for acquiring suitable air ingestion by means of soffit vents. (On top of the structure problems, there are actually troubles mainly because each of the Areas in between rafters in which they meet the best plate had been bricked in, seemingly at time of construction). Correct conventional movement-by underdeck roof ventilation are going to be difficult. After we 1st seemed into this undertaking, the setting up inspector requested us to still use vent channels (low-priced polystrene was OK) to capture whichever ventilation we could.
Positive It truly is loads of difficulty. It looks like fewer problems the detail posted as example within the weblog above and works by using no foam... Which is a "biggie" for me.
The roof seems to have a layer of asphalt shingles in excess of the sheathing by using a tin roof more than that. The soffits are closed off. The house is way off the beaten path and It is really difficult to get any why not try this out contractors in existence to work, let alone give bids so I'm basically alone.
Here is the normal answer for many who ought to comply with most building codes (the answer arises from an post by Mike Guertin):
November 18, 2011 Impression one of 3 A leaky ceiling doomed the roof sheathing. The ceiling of this 10-calendar year-previous dwelling was Minimize for an electrical box, and the outsized gap was hardly ever caulked. Dampness-laden air entered the rafter bays as a result of these cracks. When the moisture encountered cold roof sheathing, it condensed, leading to humidity accumulation and rot. (The rubberized membrane while in the Image was utilized as A short lived patch for your hole during the roof, and did not add on the failure system.) Graphic Credit: Peter Yost A leaky ceiling doomed the roof sheathing. The ceiling of the ten-year-old household was Slash for an electrical box, plus the oversized hole was under no circumstances caulked. Humidity-laden air entered the rafter bays by way of these cracks.
A. You ought to only use an set up method that your insulation contractor is informed about. Right here while in the Northeast, several contractors would almost certainly fill your rafter bays utilizing the dense-pack method just after your new roof sheathing was put in.
In the final summary it reads: "In case you are employing fluffy insulation, you need two air obstacles: one under the insulation, and one previously mentioned the insulation.
It's safe to express that an existing home does not have good roof air flow if there aren't any soffit vents or ridge vents. It's also Protected to claim that, even when there are actually pop over to this site soffit vents and ridge vents, the roof isn't ventilated if it features valleys, hips, dormers, or skylights.
If we're going to put some insulation over the ceiling, then I want to put Many of the insulation earlier mentioned the ceiling, and stay away from the Price and hassle of a whole new decreased ceiling. That means a build-up of eight", applying XPS. If we Make up the roof line higher than the cathedral ceiling on the loved ones place Get the facts by eight", we presumably want to make up the remainder of the adjoining gable roof also.
I checked out the unvented schematics and I'm not absolutely sure that fits the Invoice for up here (Canada - west coast).
Having said that, if your neighborhood making inspector approves of your respective plan, and In case you have loads of your time on the hands, and also you are capable of carrying out a meticulous career of air sealing, you could go on and try the Reduce-and-cobble method.