Anybody Know Anything About Roofs?

[al76slc]

I'm pretty sure we're near the end of the existing roof - we're about 25 years out on what I'm guessing is 25 year shingles. I see numerous nails coming up even though I hammer them down and tar them as much as I can – I can’t keep up with them. The shingles seem to be dried out - cracking and losing their flexibility. We have some leaking, although I try to keep up with it. We have a little leaking from the skylights.

However – the biggest problem I notice when I’m on the roof is the waves. It looks like the sheathing is sagging between the rafters so that the ends of the sheathing sheets are pulling up, which is causing the nails to pull out. Or there were just not enough nails put in, so that as the sheathing warps, it’s pulling up the nails and creating voids. In any case, it’s leaving us with high and low spots, and definite voids.

In this town we are permitted to lay 2 courses of shingles over the existing shingles.

Seems to me that just putting new shingles over the existing shingles without doing something about the sheathing will cause the new shingles to fail early. My thought is to pull off the existing shingles, and put down another layer of sheathing over the existing sheathing. Then – as long as I’m doing that - cover with some sort of barrier material over the sheathing. Then cover with new shingles.

Or am I over-thinking this and should I just put up new shingles over the old?

I want to do this once – we have lived here 20 years and I want to stay here

All I know is that I had to write a large check to have mine replaced a few months ago, it was 22 years old and completely shot.

There will be many many opinions on this but IMHO I never really liked the idea of just throwing shingles on top of shingles. I think you plan sounds like the best idea. Another good reason to rip of the old is so that you can install roof vents, that will help your singles last longer. And if you take off the old you can see what condition your underlayment is in. Good luck with whatever you decide to do.

[kerry]

I agree that it would not be wise to put down an additional layer of shingles over your existing roof, given the problems. I'm a big fan of metal roofs. My wife and I put one on our house 20 yrs ago and it won't have to touched again in our lifetimes and probably not in the next generations either.

[link]

The waves may be the result of a lack of ventilation.

A neighbor did a 2nd course of shingles over a failing roof. 5 years later the redo failed and the roof "leaked as often a beer belly" so was torn down to the plywood and done again. Some of the plywood was replaced and the roof was completely re-done. Classic story about the results of a half-assed repair.

All the same: Sting

[MS Fowler]

The sagging is likely caused by the original builder building "to Code". The Building Code allowed 3/8 OSB sheathing if clips were placed mid span. In my experience, 3/8 OSB is just not a good sheathing for exactly the reason to are seeing. I prefer a plywood sheathing 1/2 thick. Its a little overkill, but 25 years and my roof is flat while my neightbors all have some amount of sag.

[SwampYankee]

When we had our roof replaced about 10 years ago there was a layer of cedar shingles with 2 layers of asphalt over top. Yes, only 2 layers permitted.

[Dee8go]

Yeah, a good foundation is important no matter what you're talking about. If you're planning on staying there for a long time, I would beef up your sheathing and then put on new shingles. I would never reshingle over the old ones. When you redo your roof, that would be a good time to make sure other things are done right such as venting, drip edges, etc. You might spend more than you would have otherwise, but it is money well-spent.

[lorainfurniture]

It is all on venting.. Is your attic finished? If not, good soffit vents, and a ridge vent will do the trick..

[Zeus]

Originally Posted by al76slc

In this town we are permitted to lay 2 courses of shingles over the existing shingles.

Or am I over-thinking this and should I just put up new shingles over the old?

I want to do this once – we have lived here 20 years and I want to stay here

I ran a roofing/contracting business for a while (back when I was at university).

My thoughts -

Strip all the old shingles off, never lay new shingles over old. If you do:

• they won't seal properly to the old shingles, creating air gaps and moisture zones
• they will look unsightly as the roof's appearance will become uneven as the new shingles settle over the old, uneven surface
• the extra weight can cause sags between joists, depending on how your roof was built

Furthermore, removing the old shingles will allow you to inspect your deck. This is critical and I would never do a roof without this step. Customers would always be amazed at the (often) extensive damage to the sheeting resulting from waiting too long to replace shingles. Often, by the time you have an actual leak inside the house, the roofing sheeting will have rotted in many areas, particularly along eaves, valleys, chimney and wall flashing areas (where the step flashing has been compromised).

Not sure what your building code is there, but here builders will often use thin OSB, just minimum code. If you want to strengthen your roof, don't layer over a sagging/aged layer. It adds extra weight and isn't really effective. Your joists may have a maximum weight allowance depending on span/beam type. Remove the old sheeting and re-sheet with 5/8 spruce. This is a big job though.

As shingles age, they begin to dry out, and will shrink in size and curl at the tips. This is when you should replace them, IMO. As they continue to dry out, the gravel surface of the shingle (which gives it protection and color) will also wear off and the tar paper portion of the shingle is exposed to the elements. It will wear very quickly at this point as the sun and UV break this layer down.

I would definitely remove all the old shingles, sweep the roof clean and then thoroughly inspect the roof deck. Nail (or screw) down any loose boards, resheet where necessary. I always used spruce plywood, not OSB.

Then apply an ice/water shield membrane to the first 3' of the eaves, the rake and along any valleys and around chimneys. Apply regular roofing tar paper to the rest of the roof, using a stapler (hammer stapler with 12mm staples for most roofs). Used painted (color match to shingles) and galvanized drip edge along eaves. Apply the drip edge first over bare wood, then cover with ice and water shield. Some people apply ice and water shield over the entire roof, but this is unnecessary IMO and a waste.

I would buy a premium shingle if you can, the 3D architectural ones are popular and look nice. Since they are often dual-layered shingles, they will last a long time.

Don't skimp on roof vents. The best vent last time I checked is a multi-ridged maxflo roof vent. Make sure all bathroom exhaust vents are properly connected to the appropriate roof vent, and not venting into the attic (which will destroy and rot the sheeting).

On the shingle warranty/lifetime numbers - they aren't very accurate. Here in Ontario, a 20-yr shingle will last about 14 years. A 25 yr shingle maybe 18ish. If you are in an area with wide seasonal and temperature variations, the shingles will deteriorate faster.

Hope this helps.

P.S. If you are doing the roof yourself, rent a quality pneumatic roofing gun (I swear by Stanley Bostich) and wear a harness...it's a pain but so is landing on the ground after falling off (don't ask my how I know).

[MS Fowler]

Zeus,

Good advice, all.

I see you recommend Spruce sheathing. Good move. When I build houses a lifetime or two ago, I had one supplier ":save" me some money by substituting Southern Yellow Pine (SYP) for my subfloor sheathing. A little moisture and it warped all over the place. SYP is strong, but not particularly stable.

[Brian Carlton]

Originally Posted by MS Fowler

The sagging is likely caused by the original builder building "to Code". The Building Code allowed 3/8 OSB sheathing if clips were placed mid span. In my experience, 3/8 OSB is just not a good sheathing for exactly the reason to are seeing. I prefer a plywood sheathing 1/2 thick. Its a little overkill, but 25 years and my roof is flat while my neightbors all have some amount of sag.

X2.

About five years ago I had to replace the existing roof on this house. However, I was blessed with cedar shakes and two layers of asphalt shingles on top of that. The cedar was on top of 1x3" stringers, of course.

The work required is to strip it all the way down to the stringers...........and not damage the stringers. Then, since it's 24" on center, I used 5/8" plywood instead of the 1/2". The cost is another $1.00 per sheet. Well worth the additional cost.

It took six guys a period of two full days to do 14 squares. I used the 30 year architectural shingles...........will probably outlast me. Excellent work...........although a bit costly..........$4500. for the labor. I bought all the material and provided it to them.

[al76slc]

Thank you all for the help - it is remarkable how much knowledge is available here. Zeus especially - that was quite a post.

I did check with my building inspector, and he made some of the points mentioned here, including recommending removing the shingles. He was indifferent to whether we put new sheathing over the old, or took off the old. His only concern was that if it is an older house (which it's not), be careful of overtaxing the rafters.

We currently have a ridge vent running the length of the roof. Have these been improved on in the last 25 years, that we should think of replacing it?

We also have many skylights - so I was thinking that we should do something special around them. Up to now there have been some small manageable leaks from them, but I don't want to tempt fate.

Interestingly, he said if we remove/replace the sheathing or add a new layer, we will need a building permit. I suppose it's not a big deal and hopefully we won't be re-assessed.

[Zeus]

Originally Posted by al76slc

Thank you all for the help - it is remarkable how much knowledge is available here. Zeus especially - that was quite a post.

I did check with my building inspector, and he made some of the points mentioned here, including recommending removing the shingles. He was indifferent to whether we put new sheathing over the old, or took off the old. His only concern was that if it is an older house (which it's not), be careful of overtaxing the rafters.

We currently have a ridge vent running the length of the roof. Have these been improved on in the last 25 years, that we should think of replacing it?

We also have many skylights - so I was thinking that we should do something special around them. Up to now there have been some small manageable leaks from them, but I don't want to tempt fate.

Interestingly, he said if we remove/replace the sheathing or add a new layer, we will need a building permit. I suppose it's not a big deal and hopefully we won't be re-assessed.

Np, you are welcome!

I'm not a big fan of ridge vents, I find them problematic and prone to leaking. They have a large (long) surface area to seal, and this can be lifted by ice, etc. I would generally seal the area off (add new sheating and cap with shingles) and install a high-quality, high-flow roof vent instead. Mind you, we have nasty winters here with lots of snow and freeze/thaws...so your mileage may differ. They are probably fine in areas with little to no snow.

Skylights are always fun, especially if they were not installed correctly. The key is installation, and the flashing in particular. I like Velux skylights for this reason - excellent flashing kits. You need to install the flashing exactly as described.

If your skylights are leaking and old, you can consider replacements if your budget allows. Alternately, you may be able to either reuse and reinstall the original flashing, or purchase a new flashing kit for the existing skylight and then simply reinstall when doing the roof. If the skylight itself was in good condition, I would go this route (new flashing kit).

[Chas H]

Don't know where the OP is located, and that has bearing on the roof construction.
I recommend removing the entire roof-shingles and sheathing and inspecting the rafters. If the rafters are on proper center, then 1/2 sheathing can be used-5/8 sheathing would only be needed if the rafters are on 24" centers or you have a heavy snow load. I recommend plywood sheathing over OSB. If the pitch of the roof is steep you should consider fir plywood over southern pine as it is less slippery. Proper ventilation under the roof is important.
If you are planning to do this yourself you should thoroughly research the task at your local library.