What size should roof rafters be?

[Bob Weisner]

Hi.

Does anyone know what size lumber should be used for roof rafters? We checked the rafters on the part of my house that has the flat roof and the rafters where they meet the wall joists are only about 1 1/2 inches wide!! I thought that 2x10's would have been used , but it looks like the rafters were trimed down to that size to fit in the narrow space in the roof. the roof is 20' x 34'. There is only a couple of inches of space between the ceiling and the rafters. don't see any room for insulation. The flat roof is only 7 years old. One roof suggested changing the flat roof to a regular pitched /hip roof. Any suggestions? What really concerns me is the heavy snow load in the winter.

Thanks.

Bob

[Dave Right]

I am no expert but what I understand, should use 2 x 10 for joists but a 2 x 10 is really about 1 1/2 x 9 1/2 so that is what someone did use.

[Steve Clardy]

Construction grade 2x10's are 1x1/2 x 9 1/4". Thats the way they mill them. I remember when they were 1 5/8" thickness, and have seen some of the OLD 2x10's that were actually 2x10's.

If they are sagging, or you are concerned about the snow load, you could double up the rafters as a cheaper way other than a pitched roof. But for the long haul, less leaks, less worry about snow load, a pitched roof is the way to go. It would be an expense you would have to consider. Maybe talk to some builders in your area.

Steve:)

[Jerry Olexa]

1 1/2" is standard thicknessfor common 2X stock. A 2X4 e.g., is 1 1/2 X 3 1/2. The critical measurement in your case is the width size. Are they 2X10's or 2X8's or whatever but 1 1/2 thickness is OK and standard.

[Chris Padilla]

A pitched roof beats a flat-roof any day of the week, Bob. Just makes sense, right? Do you want a "pool" for a roof or something designed to keep it dry?? :)

[Michael Perata]

Bob

The depth of a roof /rafterjoist is measured at the point it crosses or terminates on a wall. If you only have 1.5" of joist DEPTH for a rafter 20' long, it may fail simply from its own weight. Find a really good framer, or if you can afford it, a structural engineer to take a look at the framing.

[Bob Weisner]

I don't think I explained it right. The thickness of the rafters is ok. What has got me concerned is that the width of the rafters has been narrowed down to only 1 and a half inches wide where the roof rafters meet the wall joists. I don't know why they did that, but part of the reason may be because the house was built in 1870 and there were no building codes back then in my town. I had one roofer tell me that he would not build a flat roof under those conditions because the roof is just going to fail again. He said that the right way to fix the roof is to build a hip roof with a pitch to match the existing roof on the front of the house. He also said that I should call the BUILDING INSPECTOR!!! and have him come out and look at the roof and get his opinion as to what should be done with the roof. I don't know if I want to get the building inspector involved at this point. :eek:

Bob

[Chris Padilla]

Bob,

So your rafters are tapered in their width measurement or have they just been chopped at some point along the length??? :eek: Rafters are one thing NOT to be messed with in the least. You are not even supposed to drill holes in them anywhere (like to run wires).

[Steve Clardy]

Ok Ok. Now I think we are all following you. Seems you better take your roofers advice and get someone there to check it over. Can you post a picture?
Steve

[Bob Weisner]

Looks like it was trimed down from where it meets the wall joists back up along the rafters about 6 to 8 feet of the rafters length. It gets wider as you move up the rafter, but can't figure out why someone would trim the boards down to only 1 and a half inches wide? I am suprised the roof has not fell in from the heavy snowload over the years.


Bob

[Lee Schierer]

I bet that when they laid the first rafter, they found that they had too little pitch on the roof. In order to gain pitch, they thinned the rafters over the outside wall to drop that end by 1-1/2".

Snow loads on flat roofs can be disasterous in may ways. Flat roofs also tend to leak ultimately costing more than the pitched roof in time, money and aggravation. I would go the hipped roof route if it were my home.

Lee

[Kelly C. Hanna]

You need a new roof. You cannot have just 1.5" at the bird's mouth and have a strong roof. You need a minimum of 2x10s in a snow load area if you're going to span 20'. You will need to get an inspector out to find out what you need to do to meet code. Roofs aren't a place to be screwin' around.

[Tom LaRussa]

He also said that I should call the BUILDING INSPECTOR!!! and have him come out and look at the roof and get his opinion as to what should be done with the roof. I don't know if I want to get the building inspector involved at this point. :eek:

Bob,

I agree with Kelly. I think calling the building inspector is exactly what you need to do.

Sure, they can be a pain at times, but their function is to make sure that your house doesn't collapse, burn, etc.

The only alternative I see is to call a structural engineer. I think the inspector would be cheaper.

JMHO,

Tom

[Bob Weisner]

I cut some of the drywall on the ceiling out this morning to get a better look at the problem in the daylight. I remeasured the rafters and they are about
3 1/2 inches wide approximatly 2 feet from the bedroom wall. Rafters get narrower towards the edge of the roof. About 3 to 4 feet from that, the rafters are exactly 6 inches wide. I did notice that some of the rafters have boards that are sistered together to make the rafters wider. One of the boards looks like it was notched out with an ax.

Bob

[Dan Mages]

Bob. You said that the house was built in the 1870s? These boards that you say are narrowed, do they have cut nails or wire nails? If they have wire nails, the roof has probably been redone sometime in the past, hence the difference in width.

Dan

[Bob Weisner]

I think they are just regular nails. I know that when we had the house waterproofed from the outside, they had to dig around the outside of the house to put the draintile in. When they dug in the front of the house, they hit a very old dug well that poured about 3 feet of water in the trench that they dug around the house. We did not know that there was a well there. The well that we are currently using is in our basement. It's 55 feet deep with the water at the 35 foot level. The house I believe was built in 2 stages. The older part of the house I can tell because it has 10x10 or 10 x 12 beams in the basement and the floor boards are up to 17 inches wide. The part of the basement that is towards the back of the house where the flat roof is located, has standard width lumber.

Bob