Metal Roof over Tar&Gravel: insulation
I’m planning on installing a mechanically seamed metal roof over the tar & gravel roof of my 60s California ranch. I am installing it for it’s aesthetic and for its heat reflective properties. I’ve researched the options, and I’m not interested in the other roofing materials available, just trying to find ways to get the most out of the material that I’ve chosen.
Here’s the deal: The roof on my house has almost zero insulation. The surface temp of the tongue and groove ceiling can reach 90 degrees at midday, radiating enough heat to keep the a/c running continuously for several hours. I want to build in insulation or airflow without changing the pitch of the roof (1.5 over 12), or increasing it’s thickness more than a 2-3 inches.
I’m thinking that there is a variety of materials that I could put down with the furring strips. Also, maybe there’s a way to have insulation material as well as a 1-2″ space for air circulation.
What are your thoughts on the possibilities for different materials and configurations that could result in a more efficient roof within these limitations?
thanks,
Allen Mueller
Atlanta, GA
Replies
Most tar/gravel roofs are near dead level. Most metal roofs need some slope (at least 2/12, I'd think). I seen a disconnect.
I've already addressed the pitch issue. The metal roof supplier that I am using said it's fine to install mechanically seamed roof on a pitch this low. You're referring to the more common dutch seamed metal roofs, which cannot be installed on a pitch lower than 3:12.
1) remove the BUR and gravel. Repair any bad sheathing
2) add 2 layers of 1" polyiso with the seams staggered.
3) install 7/16 osb or 1/2" cdx over the installation with the proper screws.
4) dry-in over the new sheathing with Titanium UDL or equivalent.
5) install furring over that and then
6) install roof.
You might be able to skip the furring depending on manufacturer's recommendations.
View Imagehttp://grantlogan.net/
I've never met a man that was owed as much as he thought he was.
This is just what I was looking for.
Excellent! Have you done this before?(great pics, btw...)
Have you done this before?
I primarily do copper roofs, so I don't use the furring step and don't like to install steel roofing on furring (too much opportunity to get wind underneath it), but yes I've done many. Click my website link below.
View Image
http://grantlogan.net/
I've never met a man that was owed as much as he thought he was.
Edited 8/13/2007 11:37 am ET by seeyou
Wow, that flat copper looks neat. You must enjoy your work.
That's a great portfolio, most roofing companies show alot of mediocre stuff, yours has great a few great shots that cover the gamut of what you do. Building the site yourself?(reply to image)
**spacing, punctuation and grammar skills not included.
I'm creating an illustrated article out of this project. Would you be available for quotation in the article? I think in all it will take me 8-10 months to arrive at the actual installation, so it would be awhile before it is submitted.thanks,allenmueller at comcast dot net
Would you be available for quotation in the article?
Sure, why not?
View Imagehttp://grantlogan.net/
I've never met a man that was owed as much as he thought he was.
I think I like your specs even better than mine 'cept add more insulation
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
'cept add more insulation
He stipulated that he didn't want it to be more than 3" extra height. Of course if he removed the BUR then he'd probably gain about an inch there, so I'd do two layers, 2" and 1".
Hey, you made up your mind about going north yet? I hope to see you guys and hope Mrs. N is doing OK.
View Image
http://grantlogan.net/
I've never met a man that was owed as much as he thought he was.
Your pictures keep getting better and better! I always have a free cell game running
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Most metal roofs need some slope (at least 2/12, I'd think).
That varies widely from style to style - brand to brand. The OP says he has 1.5/12.
View Imagehttp://grantlogan.net/
I've never met a man that was owed as much as he thought he was.
You need to do something about the roof on it now. No way would I go over a gravel BUR roof. Removing just the gravel is a royal PITA, so plan to strip it down to the sheathing. Then you can deal with any bad spots from past leaks if they exist.
Then apply any where from 2" to 4" of foam board - I would probably use the XPS. And lay the furring over it.
You can get long structural screws from GRK Canada that will go all the way through to hold down and then you have a base for the new metal roof.
Now, planing for how to keep water out WHILE you work is the next hurdle. You DIY or contracting this out?
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
I'll be doing it myself with the help of a few family members with metal roofing experience and a few of the guys hanging out in front of Home Depot. I was planning on getting several large tarps and doing the work during a time of the year that is least likely to have wind and rain. That way I'm covered either way.I agree about fully removing the BUR. It's been up there for too long with what appears to be no maintenance at all. Along the areas where pressure from the furring is fastened, will the foam compress over time, leaving slack and/or allowing movement?
Along the areas where pressure from the furring is fastened, will the foam compress over time, leaving slack and/or allowing movement?
Shouldn't be a problem if you cover the insulation with plywood or OSB to spread the weight.
View Imagehttp://grantlogan.net/
I've never met a man that was owed as much as he thought he was.
compression in the foam is not a concern.fro comparison info on types of foam though - SEeyou recommended polyiso I think, while I recommended the XPS or the EPS.Polyiso is open celled and will absorb moisture if the roof ever leaks or other vapor can get to it and condense. But it has a better R-value of about R-7.2 per inchThe EPS has an R-value of R-5, but it is more resistant to compression and it is a closed cell so it is totally wat6er proof.Another thing to think about as you install this stuff is having some cans of spray foam on hand. It is rare that you will cover an entire roof without some gaps here and there or a broken corner. Using a bit of the spray foam to seal those gaps will prevent convection air and the condensation that can present itself over time in those locations.
You can also use it as a glue to tack pieces in place.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
When you tear the roof off (I'm assuming it's a gable roof), start at the ridge and tear off 6'+ across the whole width. Lay a 2' wide strip of insulation (or what ever width less than 4' aloows you to wind up with a 4' width at the bottom). Lay a 2nd row of full width down to near your tear off edge.
Overlay your 2nd layer of insulation (full width) and screw down one row of full width sheathing. Nail a row of underlayment down so it laps the other side - leave the bottom edge loose. Nail a second row of underlayment at the bottom of the first so it laps onto the BUR. Flip the bottom of the top row over the second row of underlayment and nail it down. When you quit for the day all you have to do in nail the bottom edge of the underlayment to the BUR. Most of the synthetic underlayments comein 4' and 5' widths.
Then repeat the process 'til you get to the bottom.
View Image
http://grantlogan.net/
I've never met a man that was owed as much as he thought he was.
Well, the divil is in the details--what sort(s) of overhangs do you presently have?
Might take a bit of finesse to get you the roof you want with a 2 or 3 foot overhang in place. Or, if it's a a bungalow in craftsman or sears style.
Otherwise, you're already getting some of the most professional help you can.
CA is going to be a maritime climate, and you are going to get the benefits of a thermally-reflective surface for your new roof, with the added benefit of a thermal break between the exposed surface and the framing underneath. Adding ventilation is just providing a path for moisture and water vapor into your roof structure to condense or do such other evils as unchecked water moleculed will to buildings.
Now, to address edge thickness, you could contemplate tapered polyisocyanurate, but, you'd need a middling-custom order from the isoboard supplier to get your tapers gradual enough to not make for a wavy roof.
Since you are contemplating DIY with laborers, you likely will be best served with a single thickness of which ever rigid insulation board is mist economical in your area. I'd check with your roofing guy and see which products/suppliers he's worked with, and get his "read" on the various ways.
I actually live in Atlanta, GA. (The style of the architecture is Cali Ranch.) I get mixed messages when it comes to buiding airflow into the design with furring strips. Some say it will invite moistue problems, others say it will increase cooling efficiency. Sounds like I just need to use good insulation and forget about the air circ?Overhangs are broad eaves wiith 4"x8" pine beams. Design is classified as MidCentury Modern.Also, I've heard screwing/nailing the polyiso into the decking is almost impossible to do without getting some waviness, even though it's supposedly not visible once the roof goes on. Any ideas on how I can minimize this effect?
actually live in Atlanta, GA. (The style of the architecture is Cali Ranch.)
Gotcha--that's hot-humid climate, then. Humidity levels beg to be excluded from any framing contact then.
Sounds like I just need to use good insulation and forget about the air circ?
That would be my choice. It was, what 98-99 in ATL today? Hrad to imagine that 15-16 cfm of 90+º air will "cool" much of anything. I'll guess that, at your Latittude, like mine, the lowest temps are probably right at daybreak and don't even last an hour. So, an hour of 78-79º 90+% RH air is not going to "cool" things off, either.
Also, I've heard screwing/nailing the polyiso into the decking is almost impossible to do without getting some waviness, even though it's supposedly not visible once the roof goes on. Any ideas on how I can minimize this effect?
Well, the trick of it, is generally to not overdrive the screws through the big pan washers in too large an area. The standing seam will "span" some, but you don't want to count on it. That's where putting a plywood or exterior-grade osb of the foam may help you out, by adding a "flattening" layer to the sandwich.
Oh yeah, might not be a bad idea to mentally prepare yourself for a wholesale fascia repair/replace. Have you looked at you metal roofer's options for edge & drip trim? This is where real artisans, like CU & such can really get you that champagne finish on a premium beer budget.Occupational hazard of my occupation not being around (sorry Bubba)
I'll definitely exclude the air layer then.« Oh yeah, might not be a bad idea to mentally prepare yourself for a wholesale fascia repair/replace. Have you looked at you metal roofer's options for edge & drip trim? This is where real artisans, like CU & such can really get you that champagne finish on a premium beer budget. »This is something that I have just scratched the surface on. I really want to replace all the edge trim because it's poorly installed and ugly. I have to figure out the total thickness gain for the cross-section that I choose. 2" of polyiso, 7/16" OSB, underlayment looks like a thickness increase of 2.5 inches. Also to consider, if the metal edge panels leave the bottom 2" of the facia visible as on the current roof, then I am considering treating it with stain and varnish to match the tongue and groove in the eaves. I want to take my time here and make an attractive decision. (I've even considered installing lighting into the eaves for nighttime curb-appeal.)For reference, I'm considering McElroy Metal Roofing materials, because I think they are the only local supplier that also rents out the electric seamer. I really prefer Follansbee because they have a satin stainless steel product. Still haven't found out if the local supplier, JGAcorp.com, will rent an electric seamer with the purchase of Follansbee Metal Roofing products. BTW, thanks for the informative posts! There is some very intelligent people here.