Roof Slope Question

[CurlyDave]

Rebuilding my burned out house, I am having to jump through a lot of hoops the Town is putting up.

One is that in many places I can not increase the overall height of the house, not even by an inch.

The problem that I am facing is that my old roof was built 100 years ago from 2x4 rafters. To get the right insulation in I have to go to 2x10, which is 6 inches thicker. Combine this with 2x10 floor joists instead of 2x6 and a couple of other problems, and I have to lower the roof peak by ~12".

One relatively painless way to do this is to just lower the roof slope from 5 in 12 to 4 in 12.

Does anyone have any experience here. I suspect that a 4 in 12 roof is going to be more leak prone than a 5 in 12, but is it a big difference or a small one?

 

[dex3361]

4/12 is the standard in WV and I haven't had any issues with water. Most all of the trusses are built 4/12 as well. Its easier to walk on too.

 

[buckeyefarmer]

part of mine is 4/12, not that uncommon.

 

[dave1949]

Hi Dave,

I really don't know what the weather is like in your area. I don't think you should have a problem with 4/12 pitch though. Is a standing seam metal roof an option? Pre-cut or on-site formed and cut to length results in no seams except if you have a valley.

Here, where snow retention and ice damming is common, roofers put Grace brand Ice & Water Shield down first, then the roofing, even under metal if you want to have a really water proof roof and also be protected from the melt water that can back up behind an ice dam at the eaves. This is a great product, the actual roofing material is almost an after thought. Of course, it adds to the overall cost of the roof.

I have mentioned this product before, I don't have any connection to it, just believe in it.
Dave.

 

[CurlyDave]

The house is in the SF Bay area. In the past 30 years it has snowed once or twice and the snow only lasted one morning.

Rain comes through in "cells". When the cell is over you it can rain for a few minutes at a horrible rate, maybe 10" per hour, but the cell moves on after a few minutes and there is relative calm. Overall sustained max rate I have ever seen is more like 3-4" per hour and that is rare.

Cost is a big concern, as the house was for sale at the time of the fire, and will be going back on the market soon. Metal roofs are very uncommon in this area and would be a detriment. I was thinking more of 40-year composition shingles over double 30 lb. paper.

 

[Charlesaf3]

4/12 is fine, but one the edge, if that makes sense. Go ahead and do it, but cover it in grace ice and water shield and do an unvented roof assembly - google Lstibureks plans etc. Easier to build and will save you energy as well.

Under 4/12 I'd treat it like a flat roof - epdm it.

 

[JB4310]

That is a very low pitch roof, near the limit for shingles, I actually think 4/12 is the cut off point where you have to increase underpayment specs, something like 2 layers of felt needed to achieve warranty requirements.

Do you get snow, that's the killer on low slope roofs, when it's slushy due to melting and rain or when it freezes at the eaves. put the 2 of those together and you have a real potential for leaking on any roof, but more so on lower slope.

I know how those planing and zoning boards can be but they always have an option of applying for a variance, and in your case I think you have very strong grounds for them approving it, especially if it's only a few inches and it could affect the integrity of the building if not approved.
TPZ and building dept are usually pretty close to each other, I would talk to the building people who understand this stuff and if they are reasonable they may recommend to the zoning people that that's what should be done, if you're lucky maybe the building dept would require the greater pitch.

EDIT: I read you are just planning on selling and want to keep this simple, and you don't get snow.
So the easy and cheaper way to go is lower the ridge a foot like you said, you may have to double the felt, though 30 pound is pretty good stuff, that's what I used on mine. The ice and wind rubber is more for the problems associated with ice damming at the eaves and in valleys, probably don't even need it. or if you did you'd need it over the entire roof. End Edit:

Good luck, JB.

 

[Pops15]

4/12 roof pitch was the standard on ranch and tri-level homes built in the 50's, 60's, 70's and 80's here in the mid-west. I don't see any reason why you'd have any problems using that pitch as long as your flashings are done properly.
Shingle manufacturers vary on the recommended minimum pitch. Every brand that I've ever used say 4/12 is ok. Some are guaranteed on pitches as low as 3/12 but I'd suggest using an ice and water shield on the entire roof with that flat of a pitch.
ALWAYS use ice and water shield along the eaves no matter what the pitch.
Why 2 layers of 30# ? There are varying schools of thought on what weight of felt to use. 30# is popular in warmer climates. 15# works better in areas prone to hail storms (it's less "cushy" so the hail doesn't damage the shingles nearly as much). If you're going to use 2 layers of 30# why not just use one layer of 60#? Better yet why not just use ice and water shield on the entire roof?

 

[dave1949]

The house is in the SF Bay area. In the past 30 years it has snowed once or twice and the snow only lasted one morning.

Rain comes through in "cells". When the cell is over you it can rain for a few minutes at a horrible rate, maybe 10" per hour, but the cell moves on after a few minutes and there is relative calm. Overall sustained max rate I have ever seen is more like 3-4" per hour and that is rare.

Cost is a big concern, as the house was for sale at the time of the fire, and will be going back on the market soon. Metal roofs are very uncommon in this area and would be a detriment. I was thinking more of 40-year composition shingles over double 30 lb. paper.

In that case, as long as 4/12 doesn't look out of place in the surrounding homes, double 30lb and 40 yr shingles sounds like a pretty nice roof to me. I watched a stiff west wind blow heavy rain UP a valley in my 5/12 roof in Ohio once, so stuff happens. At least I found out why I had a slight leak.
Dave.

 

[bp fick]

4/12 is not the limit on shingles. As others stated, it is THE standard pitch on ranches all over America, and the simple two story "colonials" too. Compromises abound in almost every building project and having to go to a 4/12 isn't a deal breaker in any way.

It's fine. It just wouldn't be my choice for snow loading, which in your area is not a concern.

+1 on the ice and water shield, though.

 

[SuperCobra]

Rebuilding my burned out house, I am having to jump through a lot of hoops the Town is putting up.

One is that in many places I can not increase the overall height of the house, not even by an inch.

The problem that I am facing is that my old roof was built 100 years ago from 2x4 rafters. To get the right insulation in I have to go to 2x10, which is 6 inches thicker. Combine this with 2x10 floor joists instead of 2x6 and a couple of other problems, and I have to lower the roof peak by ~12".

One relatively painless way to do this is to just lower the roof slope from 5 in 12 to 4 in 12.

Does anyone have any experience here. I suspect that a 4 in 12 roof is going to be more leak prone than a 5 in 12, but is it a big difference or a small one?

Sorry if I missed a clue in another post but how does the town know how tall your 100 year old burnt out shell was? Is it still standing? Did they take a tape to it? If not, are sure sure you didn't have 2x12 rafters and 10' walls? Don't forget to include the height of the burned away pergola.

 

[winston1]

I live in Northeast Texas. Have been connected with construction on and off the last 45 years. My house is 3-1/2 and 12. Have lived in it 27 years, never leaked. We don't have problems with ice dams around here. If that could be a problem where you are you would need the ice shield the first 3 feet up. That is code I think in snow areas. Roofing felt is actually a moisture barrier that breathes. I think you can probably google and read more about it. The shingles are the rain barrier. From your post I am assuming your insulation is to be sprayed on your rafters. That is done some here but rarely. Most of ours are insulated on top of ceiling. Haven't seen your plan so might not be feasible. If it were you could go with smaller rafters.

 

[EddieWalker]

4:12 is VERY COMMON here. Probably the most common pitch by far. No snow here, but allot of rain. I cant' say that we get 10" rains in an hour, or even a day, but one to two inch downpours in an hour are fairly common, and since living here, I've seen two 5 inch rians. We get about 4 ft of rain per year hear, and it's pretty much all year round. A month without rain is extremely rare.

That said, the newer homes, higher end of things are 12:12 pitch. Lots of big roofs here!!

Once you finish with the house, I'd be very surprised if you can notice the difference from 5:12 to 4:12. I know that I've had to put a square and level on a few roofs to be sure of the pitch. When it's that close, your eyes can trick you.

Have you looked around the neighborhood and seen what the other homes have? My guess is that you'll see allot that are real close. Probably see some that you just can't be sure exacly what the pitch is on them.

Are you doing a whole envelope insulation? or a cathedral ceiling? Why the 2x10's for the insulation?

Eddie

 

[CurlyDave]

Sorry if I missed a clue in another post but how does the town know how tall your 100 year old burnt out shell was? Is it still standing? Did they take a tape to it? If not, are sure sure you didn't have 2x12 rafters and 10' walls? Don't forget to include the height of the burned away pergola.

No, they didn't take a tape to it.

The house burned, but was still standing, and as a condition of getting a permit to rebuild they made me pay for a surveyor to go out and survey the property, including heights of all the buildings and each roof surface. At first, they wanted him to survey based on height above grade and if I changed the grade at all they wanted me to get the lower of the actual height or the new height above the new grade.

I convinced them that they should accept a survey which showed the absolute elevation above sea level for each height, and that we would meet the intent of their ordinance by staying at or below the existing elevation, so I can regrade around the house without having to worry.

The house is now torn down, but the survey is the gold standard.

The surveyor marked some local reference elevations, so I can measure how high things are myself.

The house is in the People's Republic of California. If you want to know why houses are expensive there just as a few more questions.

 

[JB4310]

This explains it, 4/12 is the cusp before double underlayment required, allowing you to go down to 2/12.

http://www.gaf.com/Content/Documents/22820.pdf

JB.

 

[CurlyDave]

Are you doing a whole envelope insulation? or a cathedral ceiling? Why the 2x10's for the insulation?

I wouldn't call it a cathedral ceiling, maybe a chapel.

Due to the height limitations, we will have a bedroom and the master bath with a plate height of 7'6" with the ceiling rising to about 11'6" at the centerline of the house. The 2x10s are to get R-39 insulation in to meet energy requirements.
almost all
As hard as it was, I have decided not to document the build with pictures and a log on TBN. I wanted to, but since I am acting as my own general, time is pretty short, and being in CA, I need to get everything inspected and signed off, but I don't need pictures of every step of the progress on the internet for some lawyer to come along years later and sue me over some miniscule mistake.

We typically only get 30" or so of rain in a year, but it is all in the winter months. Always a big storm or two every year, sort of along the lines of the proverbial bovine on a flat rock.

 

[JB4310]

but I don't need pictures of every step of the progress on the internet for some lawyer to come along years later and sue me over some miniscule mistake.

Exactly,
Very good point I have been catching myself lately having to bite my tongue on certain topics where unconventional tactics may have been employed.

These threads come up now on simple google searches of the topic.
I was shocked to find links to my own ramblings when searching google for certain content.

JB

 

[PILOON]

4/12 is a standard and no problem
Around here we don't even bother remouving 4 ft of snow accumulation as long as the trusses are properly designed.
The best roofing is actually to use a good self adhesive and self sealing underlay (Grace was mentioned), but others are available.
The sales rep from IKO roofing told me that better underlay with cheeper shingles actually makes for a better roofing system.
The theory being that the underlay will never leak (self sealing and adhesive) but by its nature cannot withstand weathering, hence the shingle 'topping'.

SO; every roofing job I do has total underlay.
As I point out to my clients, the labor for the underlay is minimal as basically we simply unroll it, so it is materials only for that ultimate protection. (well almost, maybe 1 hr for most simple roofs)

Even without total coverage a good roofer would do all the eaves and overhangs as well as any knooks with membrane so how much more $$ to do a full coverage? Not much!
I even use membrane over any metal flashings because metal rusts and nail holes do end up leaking in nooks and valleys (if not tarred over + membrane is faster and cleaner)

INMHO felt underlay is useless. It deteriates and merely spreads any leaks around and away from the actual leak site.

 

[bp fick]

Codes here now require the employment of ice/water shield rather than felt paper. So the debate of single or double layer no longer applies. In some areas, it is only required for the first few feet.
YMMV but one constant is this. Keep your local inspector happy.

 

[JB4310]

Codes here now require the employment of ice/water shield rather than felt paper. So the debate of single or double layer no longer applies. In some areas, it is only required for the first few feet.
YMMV but one constant is this. Keep your local inspector happy.

If code only requires I/W shield on the eaves how does that make the use of felt not apply? and are you saying that some areas require I/W shield over the whole roof?
Not saying that's a bad thing, If it were me in an area that can get those type of wind/rain events and with such a low slope roof then that's exactly what I would do.
Preventing a single leak event would make it well worth it.

But according to that link I posted, even the manufacturer GAF doesn't recommend I/W shield on roofs were there is no threat of ice damming. and since it states that roofs between 2 and 4 pitch need 2 layers of felt, I guess that means less than 4.
4 and up would only require single layer? Well one thing for sure less than 4/12 is considered low pitch and where special consideration to underpayment specs comes into play.

SO; every roofing job I do has total underlay.
As I point out to my clients, the labor for the underlay is minimal as basically we simply unroll it, so it is materials only for that ultimate protection. (well almost, maybe 1 hr for most simple roofs)

INMHO felt underlay is useless. It deteriorates and merely spreads any leaks around and away from the actual leak site.

I agree with you on the total underlay for those lower slope roofs, not gaining anything though on steeper ones just added expense IMO.

I don't agree with you on felt being useless, even 15 pound felt will last the life of the shingles, for sure if it's done in a double coverage layout, but 30# is really tuff stuff and is more than adequate for MOST shingle roofing applications.

The steeper the pitch the less the underlayment matters, look at a thatch roof, made of grass and can last longer than shingles, but it has to be steep enough to shed the water quickly.

No felt isn't perfect but it has been the go to material for a long time.
The one area we see felt in a completely failed state is on the slate roofs we work on. After 80 to 120 years especially on the south sides it literally turns to dust and pretty much just leaves a black residue/dust, making those roofs susceptible to wind and ice causing leaks, even as steep as they are.

JB.