Decking predicament

Dave Moulton
7/21/2015
Hi there, I've just ordered my metal roof package. The estimator at the store insists that the best method is to strip the shingles, use a synthetic underlay, and fasten my metal directly to the roof, provided I have 1/2 inch plywood decking. The problem is, today I found that my decking is only 3/8 plywood, trusses spaced at 16 inches ( except for the addition to the garage which is spaced at 24 inches.) estimator says by far the best solution is to lay new 1/2 inch plywood over the existing plywood. I agree, but this is going to cost me close to an extra 3000 bucks, which I am not ready to pay. If I can get away with strapping the roof, I think it will be much more affordable. Is it a good idea to use 1x4 strapping, or should I consider 2x4? I need a solution that will not cost me thousands of additional dollars! Thanks
Eric Novotny
An informed customer is the Best Customer!
7/21/2015
Strapping the roof would help with the structural stability of the roof as well as provide an above deck vent (depending on how its done).
Guest User
7/21/2015
Thanks for the reply. I'm going to do some sort of strapping. Now I'm just not sure whether do use 1x4, 2x4, or I've been considering possibly running vertical 1x2 straps with 1x4 over it horizontally to eliminate the issue of moisture buildup along the horizontal strapping. Any thoughts on this possibility?
Eric Novotny
An informed customer is the Best Customer!
7/22/2015
Try to have a minimum of a +1" vent space above the deck. It will make the convection easier.
Guest User
7/22/2015
Hi Dave, Are you planning on adding the strapping over the existing shingle or stripping the shingles off and then strap?
Guest User
7/23/2015
I'm removing the shingles and putting down ice/water shield over the whole roof. Might sound overkill, but It was only $400 more for ice/water shield than novashield membrane, so I went with it.
Todd Miller
Isaiah Industries, Inc.
7/23/2015
Dave Moulten, do you have decent attic ventilation?
Guest User
7/23/2015
Hi Todd, As far as I know there's never been ventilation issues. I'll be installing a roll vent on the ridge, and the soffits look in good shape. The insulation is piled high in there as well. Any input on my strapping situation? Thanks Dave
Todd Miller
Isaiah Industries, Inc.
7/23/2015
Good. My concern was just that ice and watershield really seals up a house ... and could create condensation issues in the attic if you don't have good ventilation. I am not so much a fan of strapping ... but I understand your situation and feels it's fine.I don't think the size of strapping is a huge issue ... just make sure that your metal roof manufacturer is okay with whatever you decide to use.
Guest User
7/24/2015
Hi Dave, I agree with Todd, that Ice and Water Shield membranes act as vapor barrier and vapor barriers are usually installed on the warm side of your roof (6mil poly behind the drywalls). I'd rather you use High Temp. Ice and Water Shield on the first 3 to 6 feet from the eaves, depending on the roof pitch, 18" on the gable ends and 36" around the valleys, and use synthetic underlayment on the rest of the roof. If your roof is a low slope, less than 4/12, and have dormers, valleys, skylights ,roof penetrations, then Ice and Water Shield becomes a necessity on the whole roof providing that you have good attic ventilation.
Eric Novotny
An informed customer is the Best Customer!
7/24/2015
I would skip the ice and water over the whole deck. Just makes pulling it up a pain if you ever have to and it is largely unnecessary in this case. If you have good attic ventilation and sufficient insulation (better yet a well air sealed attic), the probability of condensation issues are next to none. Putting in for an above deck type of venting will further decrease that potential as well as help with any attic temperature impact in the summer months. It will hurt your wintertime performance by eliminating any radiant heat gain but your ice formation should be zero at that point as well. Permeability ratings on a vented attic (as it pertains to the roof deck) are inconsequential.
Guest User
7/29/2015
Hello again, Okay the figuring is mostly done and I've gotten to work now. I want to clear up one thing before I get to it. I'm doing horizontal 1x4 strapping across my roof which I've stripped and put down ice/water shield. Along the eave edge, I'll have the strap flush with my fascia, but I don't quite know whether the drip edge should go on top of the 1x4 or if I should install my drip edge flat to the membrane and place my strap on top of that. Any suggestions? I included a picture of the house/garage just for a basic idea what my place looks like. Thanks, this has been a great resource for my project!
Eric Novotny
An informed customer is the Best Customer!
7/30/2015
The ice/water should wrap over the fascia board and the starter/drip edge should be on top of the purlins and pointed into the gutter.
Guest User
7/30/2015
Thanks Eric. And the purlin is my 1x4 I gather.
Eric Novotny
An informed customer is the Best Customer!
7/31/2015
Not sure how you have the roof laid out or what you are using for purlins/battens.
Guest User
8/1/2015
Thanks for the reply. I've been looking at my materials and ran into a problem. When planning my roof, I was speaking with an estimator at the hardware store who was was running me through what I need. As shown in the picture, he put this roof edge on my order. I assumed him to be correct given his 40 years of experience, but it appears as though this is not the correct size. Even on top of my 1x4 strapping, the vertical edge of the trim will hit the bottom inside of the gutter. This vertical edge of the metal is 4 1/2 inch, when it seems to me it should only be around 2-2/12 inches. The front run of my eaves is 80 feet long, and even if I run the gutters both directions down from the centre, I would only have an inch of slope over 40ft, and my fascia will be almost entirely covered. It seems to me I should have shorter roof edge that doesn't go as far into the gutter so that I can start my gutter at the top of the fascia and slope it as needed towards the downspout. I will be talking to the estimator on Tuesday but until then I am going to hit a standstill. Can you guys confirm my suspicion that I have the wrong material here?
Todd Miller
Isaiah Industries, Inc.
8/1/2015
That looks more like a commercial or agricultural drip edge. You do not need something that large.
Eric Novotny
An informed customer is the Best Customer!
8/2/2015
Do you have access to a brake? If so, make your own.

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