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Old 08-29-2011, 06:59 PM   #1
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Plywood over shiplap


Hello all,

I have a early 50's ranch with a low (3in12) slope, old 3-tabs and a 1x6 shiplap deck. I had a couple small leaks show up this past winter and need a new roof. The estimates I have received from roofers all suggest laying 1/2" CDX over existing shiplap deck. I have been in the attic many times and can see the shiplap is in good condition, with minimal repairs necessary. I asked one of the roofers to re-write the estimate without plywood. He replied that he strongly discourages this given the slope of my roof. I am planning on putting in additional vents, metal W valley flashing, ice&water in all valleys and eaves and putting on "lifetime" architectural shingles. My question: is the re-deck necessary due to slope, even though the shiplap is in good condition?

Thanks in advance!

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Old 08-29-2011, 10:39 PM   #2
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Plywood over shiplap


I have put on roofs with a 4/12 on 1x's (1"x6,8" etc)for decking.

Never had a problem.

If a roof is installed according to manufacture specs and your building codes then you shoul have zero to worry about.

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Old 08-29-2011, 11:30 PM   #3
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Plywood over shiplap


Not only would I suggest you find another roofer, I wouldn't let this clown back on the property. This guy is obviously attempting to scam you. There are thousands of houses around here with 3/12 pitch roofs with 1x8 shiplap decks and no, plywood or osb is not required.
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Old 08-30-2011, 01:02 AM   #4
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Plywood over shiplap


I honestly can't believe 60yr old shiplap being in "good" condition. Sure it may not be falling in, but can you hit it with a 12 gauge shingle nail without it splitting? Heck can you hit it with a hammer without it splitting?
There will be about 7000 nails going into your roof, how many split pieces of shiplap are you ok with? And are you going to complain if after your roof is done, you look in the attic and see all sorts of broken shiplap?

We won't do a ship lap roof unless we sheet it first. It has nothing to do with slope either. 60 yr old shiplap roofs around here are brittle like stained glass, you show it your tear-off tool and you can here it cracking.

That and you don't need "w" valley metal on a 3/12, water won't be flowing that fast.
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Old 08-30-2011, 03:06 AM   #5
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Plywood over shiplap


Bcdemon, where is "around here"? I am in portland, or. I would guess weather plays a significant roll in aging shiplap, not sure how different our weather is or how big of a difference it makes but I thought I'd mention it.

The shiplap does look like its in good condition, however I haven't put nails into it or given it any other test of strength. Thanks for the heads up.

As for slope, I haven't actually measured it. I was low balling it to see if indeed, as the roofer said, low slopes necessitate adding plywood over shiplap. I am guessing it is actually a 4 in 12 slope, maybe more. What is the minimum slope you would recommend using "w" valley flashing on?

Thanks for the replies.
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Old 08-30-2011, 06:40 AM   #6
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Plywood over shiplap


I'm not sure about other regions either but in my portion of the mid west 'Ohio, 60 year old strip sheathing is as strong or stronger then brand new plywood sheathing.

The most recent re-roof over strip sheathing I did was a couple months ago,
that home was built in 1928 and I did not replace one single piece of sheathing, all tho I did re-nail every board.
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Old 08-30-2011, 09:24 AM   #7
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Plywood over shiplap


Quote:
Originally Posted by diyroofer View Post
Bcdemon, where is "around here"? I am in portland, or. I would guess weather plays a significant roll in aging shiplap, not sure how different our weather is or how big of a difference it makes but I thought I'd mention it.

The shiplap does look like its in good condition, however I haven't put nails into it or given it any other test of strength. Thanks for the heads up.

As for slope, I haven't actually measured it. I was low balling it to see if indeed, as the roofer said, low slopes necessitate adding plywood over shiplap. I am guessing it is actually a 4 in 12 slope, maybe more. What is the minimum slope you would recommend using "w" valley flashing on?

Thanks for the replies.
Around here being Kamloops BC, Canada. We have a very hot climate in the summer, and an average Canadian winter climate. The issue with shiplap here is that it dries out and gets brittle. So when you try to nail it with a roofing nail, it splits. Not every time, but one incorrect nail is all it takes.

We use regular valley metal for upto 6/12, after that we start using "W" metal. Or if we had say a 4/12 and 9/12 valley combo. The benefit of the "W" is to stop water from one side of the valley getting under the opposite side.
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Old 08-30-2011, 01:45 PM   #8
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Plywood over shiplap


Great, thanks again for the info guys. I have a few friends with a fair amount of roofing experience and if I can't find a reputable roofer who will do it without the new deck I may do it myself. I accept the risks.

Bcdemon, you referred to incorrect nailing as a common reason for ship lap splitting/cracking. Are you referring to nail location on the board, i.e. out on the edge, or does it have more to do with angle of entry and/or force applied? If I do it myself I am planning on hand nailing to avoid over and under driving nails due to variability of wood density. The roof is only 15 square, so I don't think hand nailing will add a huge amount of time.
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Old 08-30-2011, 02:27 PM   #9
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Plywood over shiplap


Check the install instructions on the shingles and the underlayment being used. I&W requires a smooth, clean, dry surface. Warranty could be voided on the shingles also if the wood is not good enough for "proper installation".

I cannot give an honest answer without seeing it, but usually it's best to resheath over old 1x boards. For the cost difference, I think it's worth it....only if it's done properly. If you can't find anyone that will shingle it without resheathing, then it probably is not suitable for shingles. In this economy, most guys will do whatever the homeowner wants. If they won't, then they obviously don't want to deal with it because the 1x deck isn't good enough.

I really don't see how selling a better roof is a "scam". Does everyone think Contractors are all scam artists?

You are already putting up good materials, why not spend a few bucks and get it done right?
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Old 08-30-2011, 02:30 PM   #10
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Plywood over shiplap


There also may be a chance that the Contractors want to I&W the whole roof, or the majority of it being it has a low slope. Could be why they want a clean, dry, smooth surface.
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Old 08-30-2011, 02:51 PM   #11
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Plywood over shiplap


They don't want to i&w the whole roof, just the eaves and valleys. And there is no way they can determine the condition of the shiplap since they haven't seen it. I think it will just be a lot easier for them with a re deck (they don't have to worry about driving nails between boards, etc), plus they make more money.

The shingles I am looking at require shiplap to be either 6 or 8 inch, no more than 1/8 gap between boards, and obviously they have to be secured to rafters, flush, and without rot.

Looking in the garage (it is attached and has the same roof), there is only one space bigger than 1/8", for about a five foot span. I think the boards are even tighter on the house roof.

Another issue I am running into is ventilation. Roofers want to cut in a bunch of turtle vents...I would like ridge and eave vents. However, I have a overhang with no soffit, just the shiplap on the rafters. I was thinking of putting vents in the "fascia". On a side note, I am not sure if the board I am referring to is actually fascia. since there is a true fascia board the gutter is mounted to, then the overhang, then a 2x board that is above the siding, under the overhang and spans between rafters...what is the proper name for this?
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Old 08-31-2011, 09:02 AM   #12
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Plywood over shiplap


When I said "1 incorrect nail is all it takes" I meant if just 1 nail blows through the roof without the roofer noticing, manufacturer can void warranty.

And don't think that the roofing company is going to make a mint off sheathing your roof. They may make a few extra bucks, but they also want to leave a quality job behind. And trust me, it would be a lot easier to just tear and shingle than it would be to tear, re-sheet and then shingle.
You say your shiplap is fine, how many other shiplap roofs have you inspected?

Soffit vent:
You could cut out a 6x9 hole in your soffit and install a soffit vent, well a few of them.
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Old 08-31-2011, 12:34 PM   #13
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Plywood over shiplap


I took a bunch of pictures of the shiplap from inside my attic, but didn't upload from my camera, i will put a couple up tonight...i would like to hear opinions on it. While searching around forums, etc... I have seen as many say that re-decking is essential, as there are who say it is unnecessary. I am not going to be in the house that long, and if I have to transfer a roof to a new homeowner that will expire 10 years early because I didn't spend 1500 on a new deck, then so be it. However, if I am going to see leaks in the next 5 years simply because it didn't get re-decked, then I would spend the money.

As far as the vents go, I have open cornice overhangs. So I cannot vent the soffit. I will have to either install venting into the blocking (that sits above the wall, between the rafters), or I will have to install a mid-roof smartvent or coravent type product. There are two lengths of the blocking totally removed and replaced with 1/4" screen on one side of the house, but that is the only venting down low. Since there are two ridges (a North-South and East-West, with the N-S ridge intersecting the E-W ridge at the midpoint) there are three gable vents and five 11 inch mushroom vents in the existing roof...wondering if I should do the calcs and add to existing ventilation if needed or cover existing and put in an eave and ridge type vent system.

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