Replies

1. 
   p_vilefort | May 08, 2022 03:03am | #1

   You are correct in saying that powered attic ventilating fans are a waste of money and electricity. Stick to your guns and if you can find the BSI article show it to them. If you have a continuous soffit vent on the south side and one on the north, however long it can be then you should be fine. The end vents aren't necessary and can create future problems with small birds getting in when the screening fails. If you want some end venting possibility install a window in the end walls. They will allow light into the attic space and can be used for venting if necessary. There is a new procedure for installing windows today.
   The other option is to condition the attic space. What that means is there is no venting to the outside and to control vapor getting into the attic you must seal all of the spaces leading from the lower floor into the attic. Once you seal all of the air entry points into the attic you will insulate the end walls with something like Rockwool R-13 insulation. It is moisture resistant and fireproof. You could also use rockwool in the ceiling joist bays that make up the floor in the attic space. If you want to keep some venting in case there is a future roof leak, you can put foil-faced polyiso board insulation on the bottom edges of the roof rafters covering the entire interior of the attic space including sealing off the ridge vent. Remember the soffit is open allowing air to enter and rise to the ridge vent to exhaust. This air space is now between the insulation board and the underside of the roof. You will also need to use some insulation board to seal off the ceiling bays from the soffits. When I did this I used the insulation board and 3M fireproof sealant caulking (red color). I also used this caulking to seal air venting from plumbing and electrical wires coming from the living space to the attic. There is a book you can get from Fine Homebuilding that explains with pictures how to do all this. The title is "The Energy-Smart House".
   If you really want to improve the insulation on your home insulate the roof on the outside. Apply two layers of 2 inch thick polyiso aluminum faced insulation board over the original sheathing. From when the house was originally built it may have 3/4 inch or 1 inch thick ship lap sheathing. The seams where the sheathing boards are butted together should be taped to make them air tight and the insulation board should be secured to the roof underlayment with screws. Seams in the two layers of insulation board should be offset, not lined up. There are plastic washers that can be used under the screw heads to spread the force on the insulation board. On top of the insulation board should be a layer of OSB or plywood. The best material to use under the insulation and on top of the roof sheathing is a peel and stick material that is usually used near the end of the roof or in valleys. The best application is to cover the entire roof with taped seams or a minimum 4 inch overlap. This layer should be rolled if specified by the manufacturer. Some use a pressure sensitive mastic and rolling the material in place is necessary. This is far superior to any tar paper. Then comes the insulation board and then the additional layer of plywood or OSB. I prefer plywood because it is more resistant to the effects of water exposure. The seams between the plywood should be sealed with a peel and stick the same stuff used on the sheathing but cut into 4 inch wide strips. This final layer of wood should be screwed to the original roof structure, preferably into the roof rafters. You will probably need 6 inch long screws to penetrate all the way into the original rafters or original sheathing.
   Are you going with a metal roof? In your picture the building to the right isn't part of your house is it? If it isn't then your roof is simple and lends it to a metal roof covering. The only additional thing you need with a metal roof are furring strips to allow any water that gets blown in, a way to get out. Furring strips are placed diagonally and the metal roof is screwed to the furring strips. The furring strips are screwed to the OSB or plywood underneath the furring strips or into the original sheathing. For your roof I would use the 3 foot wide galvalume metal roof panels with two or more ribs and they are long enough to cover your south facing roof from the eave to the ridge. The roof I am thinking of uses hidden fasteners with raised seams. Use stainless steel screws throughout. Because your roof is simple the metal roof shouldn't cost much more than an asphalt shingle roof and will last anywhere from 70 to 100 years. There are a minimum of additional flashing pieces for this metal roof that are along the sloping edges of the roof, the ridge, and around penetrations such as vents and a chimney. Regarding vents; combine them into one if possible in the attic so you only have one penetration to flash. Vents are only for air so they can be combined without affecting their function. Fewer penetrations mean fewer places that can leak. Any laps in the roof panels should be sealed with a mastic tape made for that purpose.

1. 
   jmcnamara | May 08, 2022 07:41am | #2

   Thanks for putting so much thought put into my question P.V.
   My ignorance & inexperience has made things difficult & time is not on my side now.

   As things stand, I have put the cart before the horse as my insulators are done removing the old insulation and tons of soot/debris & coming in one week to blow in cellulose. I’m loathe to delay them but the decision to re-roof has upended venting strategy.

   This company had planned to add 2 slant back vents on the southern side (photo is northern side) to get to balanced venting but when I relayed that a roofer (a last minute notion to look at re-roofing) suggested the CertainTeed system, they were very willing to change the plan.
   A 2nd roofer,( the attic-fan guys) want to cut in soffits 2 ft apart under the southern eave only, that the northern is too narrow. Unlike roofer #1, this time they walked the roof & went into the attic noticing poor flashing integration, concern about gap(s) in the eastern fascia, unacceptable spreading in the decking boards, & water intrusion at the chimnies (not surprising).
   As I write this, it seems I may need to delay the insulators (god knows when they can pencil me in later) as I get this sorted. Ugh.

   
2. 
   jmcnamara | May 08, 2022 07:57am | #3

   Addressing your suggestions PV, my goals are still evolving here. A vented, well-insulated attic, architectural shingles, &….that’s it at the present. But I’m interested in re-examining that “plan”. It means stopping the project which worries me, but that might be the best move….