| Author | Message | ||
     Old_school (Old_school) Senior Member Username: Old_school Post Number: 1193 Registered: 01-2009 |
That makes sense then. I do like the idea of leaving the urethane off from the bottom of the roof boards. You may be just a well off putting some felt on the bottom of the roof deck and spraying though--if you use closed sell. | ||
| Zxttfan (Zxttfan) New member Username: Zxttfan Post Number: 2 Registered: 03-2015 |
Our original thought was to install baffles on all the rafters from the floor to the ridge and then spray it all-hence a baffled rafter. This is primarily to create a conditioned space for the HVAC. We're now leaning toward spraying from the floor to the top of the living space wall (including ceiling) and leaving the remaining space above unconditioned. Any ducting in that area will be insulated. As far HVAC equipment, we have an initial bid of a 100k BTU 95% furnace and 13 Seer 5 ton A/C. This is for both the 2nd and 3rd floor, about 3100 sq ft. | ||
| Old_school (Old_school) Senior Member Username: Old_school Post Number: 1192 Registered: 01-2009 |
The felt doesn't change anything with the ventilation. IF you are installing a vented soffit, and IF you have air channels beneath the roof deck from the soffit to the "attic" area above or on top of the "A", the soffit vents will become the intake and the gable ends will be the exhaust. You can make the gable end vents as large as the top triangle if you want to. They will let the air pass through and suck the air up from the soffits to keep everything moving. DON'T use a ridge vent and gable end vents as that will short circuit the air flow. Ridge vent or gable vents, but not both. I am not sure what you are talking about when you say the "baffled" rafters. Wherever you are going to be making living space, insulate it. You are going to be having some dead areas where the valley comes together, and there is no way to ventilate this. Technically, if you use a closed cell foam, it is a barrier and no ventilation is needed.It would be a good thing to keep the space between the foam and the bottom of the deck however. As far as the heating and cooling equipment, what does the manufacturer recommend? | ||
| Zxttfan (Zxttfan) New member Username: Zxttfan Post Number: 1 Registered: 03-2015 |
Hello, We are in the planning process of finishing our 3rd floor attic and are looking at spray foam for insulation. I've read a fair amount of threads on the site but have a few questions. The layout is essentially a "T" (satellite image) with the two short lines facing North and South with the long line facing East. Our side section plan is an "A" with living area below and open attic above. Total sq ft is approx. 1,100. 1. Our slate roof was replaced due to hail in 2006. The roofer added felt paper at this time. It has the original open board decking. Does this change the air gap size when installing baffles? 2. We are adding soffit vents and gable vents but weren't planning on a ridge vent. How do we determine the correct gable vent sizing? Is a ridge vent necessary with gable vents? 3. Should we spray all the baffled rafters or should we spray just the areas surrounding the 3rd floor building envelope? I suspect access will be a problem for the sprayer. In addition, both heating and cooling for the 2nd and 3rd floors will be located in this area. I assume conditioned space would be preferred. 4. Open or Closed Cell? What else should I be taking into account before we start? Is there a good option to foam in this instance? Perron | ||
| Old_school (Old_school) Senior Member Username: Old_school Post Number: 1188 Registered: 01-2009 |
Well, a couple of things. If the "insulation" is between the rafters already, how would you determine if there is any water coming in? The urethane is just a better grade of insulation, so nothing changes. If it is leaking, the water will show up somewhere, just perhaps not directly beneath the leaking point. It sounds like you could just leave the existing insulation in place and spray the urethane over it. this would keep the urethane off from the bottom of the roof deck and also off from any of the bottom of the slates. The roof would then continue to breathe as it always has. You will probably have to cover over the urethane inside the attic for fire reasons, but again, that changes nothing. As far as the slate roof goes, read Joe's book and learn all you can about it, and if you have any questions about your roof or possible leakage, just take a picture and post it on here and ask us. We will be able to tell you when to fix it and when to replace it. Good luck. | ||
| Dcattic (Dcattic) New member Username: Dcattic Post Number: 3 Registered: 08-2016 |
The old original insulation is between the rafters. Here is what our contractor said about the temperature setting: "You will want to set your thermostat to 78 degrees. That does not mean the entire house will be that temperature. The basement will probably be cooler and the attic warmer. It has been determined by those who test these things, that 78 degrees is the ideal setting to achieve the best combination of energy efficiency, humidity control, and personal comfort. A lower setting may be a little more comfortable but comes at a loss of efficiency while a higher setting saves energy but allows the humidity levels to get too high in the house, which can lead to moisture and mildew problems. When you use foam insulation you not only insulate but air seal as well. If there is too much humidity in the house and it cannot escape, you will end up with condensation and mold." We're still wondering how we would know if there was a leak in the slate roof using foam insulation and if the slate roof to be ventilated. Thank you. | ||
| Old_school (Old_school) Senior Member Username: Old_school Post Number: 1187 Registered: 01-2009 |
Where now? Under the floor or between the rafters? If you don't know why he wants it at 78 degrees, I would suggest that you ask him why! | ||
| Dcattic (Dcattic) New member Username: Dcattic Post Number: 2 Registered: 08-2016 |
The icynene will go into the rafters, not the floor. The original insulation, wool under cardboard, is there now. We are wondering if the contractor says we have to keep the attic at 78 degrees because of potential moisture problems, which means we will have to add air conditioning and heat. And how would we know if the slate failed somewhere, if the foam is covering it up inside? Thank you. | ||
| Old_school (Old_school) Senior Member Username: Old_school Post Number: 1185 Registered: 01-2009 |
Is he going to spray it on the floor or on the ceiling between the rafters? If it is on the floor, nothing really changes. If it is between the rafters, why? There is nothing there right now, correct? | ||
| Dcattic (Dcattic) New member Username: Dcattic Post Number: 1 Registered: 08-2016 |
Hello, We have a 1931 house and the original attic insulation needs to be replaced. We put on a new slate roof in 2005 using Vermont grey slate. We have our upper AC unit in the attic (for the second floor of the house), but currently no heat or cooling in the attic. The attic is used for storage. Our contractor is proposing either open cell or closed cell Icynene spray foam. He said we must keep the attic at 78 degrees, so we assume we must cool and heat it. We are concerned about both foams given what we have read about moisture problems and wonder how well they work with a slate roof. Are there any insulation alternatives? Any suggestions would be appreciated. Thank you. | ||
| Bob_wewer (Bob_wewer) New member Username: Bob_wewer Post Number: 10 Registered: 11-2013 |
The"Warm Roof Deck" has been used for years in the low sloped roofing industry. The modern asphalt roofing shingle mentality has skewed out perception. Asphalt shingles must transfer the heat from the sun into the attic in order to prevent overheating of the shingles. Natural roofing has a different dynamic. Natural roofing, except for cedar which needs to dry from the underside, can take the heat. Slate and tile actually ventilate themselves to some degree. The problem with insulating behind the roof will lie in the uniformity of the insulation and the air seal because of the interior moisture. The conditioned space must be totally sealed off from the insulation or the spray foam must be tight. This is my take after 35 yrs. in this business. | ||
| Old_school (Old_school) Senior Member Username: Old_school Post Number: 759 Registered: 01-2009 |
Steward, look at the date on the post. It is from 6 years ago. I am sure the problem is long gone already. | ||
| Steward (Steward) New member Username: Steward Post Number: 1 Registered: 01-2012 |
Moonraker, Does tri iso super 9, allow for venting from the soffit? If not, I don't understand your post. Maybe we're talking about two different animals between there and VT and our insulation requirements. | ||
| Holly Gates |
Hello, I am having icynene foam sprayed in my attic to insulate my 1890's house with a slate roof. There are two options: 1) spray between rafters directly onto underside of roof decking, possibly add VB afterwards 2) spray attic floor between joists I would sort of prefer to do #1, since then all my wiring wouldn't be buried in foam, and for a few other reasons. However I am a bit concerned about roof ventilation, moisture issues etc. The attic has no vents in it, soffits unvented, and the roofdeck is solid wood boards. Does anyone anticipate problems if I sray foam up against the deck? I suppose I could put in the baffles to leave airspace in there, but there doesn't seem to be much point if there are no soffit and ridge vents... Thanks for any suggestions! -Holly Gates Somerville, MA | ||
| Anonymous |
I would use roll insulation (r-38) with styro-foam baffels. If? you use spray foam how will you create an air-flow? | ||
| Moonraker |
Sheer and utter madness!!! If you get any leaks water will get into decking and rafters with no escape. Ideal conditions for first wet then dry rot. You will be guaranteed a major roof construction job ten to fifteen years down the line.You will also earn the undying hatred of the poor saps whose job will be to hack the wretched stuff out. | ||
| Barry Smith |
Holly, I'm planning to have polyurathane foam sprayed to the underside of my roof which I plan on slating in a couple of years. The foam guys assure me that there is no need to ventilate at all with this stuff, but I am going to anyway. I plan to use lathe or something similar nailed to the sides of each rafter to make a spacer about 1 1/2 inches wide, then attach a sheet of something, old paneling, or whatever to close in the vent space, just like the foam baffles mentioned above, only a little heavier duty. Then the foam will be sprayed onto this. In my case, I have soffit and ridge vents, but if I didn't, then I would add them. Even if those guys are right about ventilation being unnecessary, which I'm not sure about, I wouldn't want the foam on the underside of the sheeting because of the headaches if some sheeting boards needed to be replaced. | ||
| mjh |
I agree with Moonraker about it being "Sheer and utter madness" as far as Holly's idea goes. However, Barry Smith's solution sounds fine. The sarking boards will vent naturaly through the slates and the air gap between the boards and the insulation means that both sides of the boards will be vented. | ||
| Moonraker |
In England for the past two years we have been using Tri Iso Super 9. This is a laminated foil quilt,3/4 inches thick ,equivalent to 10 inches thickness of fibreglass. You can either staple it to underside or in over rafter application, with counterbattens then battens (English style ) it is made by a french company called Actis. Quick and easy to install, but expensive |
