Roof Truss Design Help

pburchett · Nov 2, 2023

Which truss design is most suitable for a 15' x 26' building constructed on 16" centers with a monolithic slab foundation?

There will be no truss overhang on the loadbearing walls.

Trusses will be placed on 2' centers with 2x4 purlins on 24" centers, and covered with a vapor barrier and agricultural metal roofing.

This is in an area with no snow load but with the occasional wind load due to its location on the eastern coast of North Carolin.

There is no storage planned above the trusses

Bob Bancroft · Nov 2, 2023

You're going to build your own trusses? Here in central NY they can be purchased so reasonably that most are purchased. And when
using 2x4 purlins, most trusses are on 4 foot centers, even with our snow load.

jimgraycase · Nov 2, 2023

I always make my trusses and I make them like your #2 design. They have worked well for me over the years, I live in a 60# snow
load zone, as well.

Destroked 450 · Nov 2, 2023

Trusses I purchased have been #1 design

MarkB_MI · Nov 3, 2023

I doubt there's a significant difference in strength between the two. The maximum bending moments will be in the centers of the 2x4s, not on their ends.

Hopefully you have some sort of engineering data you're using to design your trusses or rafters. It's available online or in any good carpentry textbook. Personally, I'd never construct a building without a roof overhang, but that's just me.

sms · Nov 3, 2023

Often the #1 design, raised heal, is used
to give room for insulation to the outside
of the wall. In upstate NY they are most
often required now with blocking between
on the outside edge.

Geo-TH,In · Nov 3, 2023

Personally, I'd never construct a building without a roof overhang. X2

You need a roof overhang to have eve ventilation.

There is a rule of thumb to have a certain amount of ventilation per square foot.

If you are building a pole barn without ventilation, you will be asking how to prevent condensation.

Menards has a truss factory in Terre Haute.

If you do the math, you may find buying trusses is cheaper than building your own.

caterpillar guy · Nov 3, 2023

We have always built our own with Full cut 2x6 and 2x4 for the brace pieces. Made from Red or White Oak,Elm, Ash,And Soft maple or Walnut. Walnut is as plentiful as Oak for us and if we cut the lumber just another stick. It has been so mlong since we have built trusses I for get which we used though I believe it was the first picture. IF we want more eave we just nail a 2x4 or 2x6 to the side of the truss and stick it out what we need. They have been there for close to 50years or more now so not a weakness. I would not want less than about 2 feet of eave overhang though just so water and snow which you said you don't have would not build up along the walls. We have I believe a 30 LBS snow load rating here. None of our buildings have fell in from snow so I guess they are strong enough.

Hemmjo · Nov 3, 2023

It you need a building permit for this project, you will need an
engineers stamp on the truss drawing.

Menards has a truss ordering page you can access online. I
recommend you look in that. You can not buy the same quality
lumber that truss manufacturers use locally.

The roof is the most important part of you structure. You building is
not that large price purchased trusses before you spend time building
an inferior product. This is NOT a reflection on your skills as a
carpenter. It has to do with them being set up to manufacture
efficiently, access to better materials, time savings for you.

I can make nice looking nuts and bolts, forge cool looking nails, but it
is mores cost effective and better use of time to purchase them.

Just consider it. If you choose to build your own. Use design #1. But
first go to menards web site and get a quote. You will get a drawing
of the truss design.

Stephen Newell · Nov 3, 2023

On 16 centers #1 would be plenty sufficient. If it were me though I would make one heavy truss more similar to #2 in the center and run purlins between.

MarkB_MI · Nov 3, 2023

> You need a roof overhang to have eve [sic] ventilation.

Yes, and it's nice to keep rainwater away from the building.

> If you do the math, you may find buying trusses is cheaper than building your own.

Where I live, the building inspector wants to see a drawing of the trusses stamped by a licensed Professional Engineer. No tickee, no washee.

MarkB_MI · Nov 3, 2023

Here are a number of truss drawings, courtesy of North Dakota State University.
NDSU building plans

wp6529 · Nov 3, 2023

I would certainly recommend purchasing over building them yourself. You will save money and labor and will have engineering backing for them. There is no savings building them yourself unless you perhaps have already milled your own lumber from your own trees. Also recommend at least a small overhang like 12" to allow for ventilation.

Texasmark · Nov 3, 2023

Agree and they will probably carry the design engineer's stamp. I don't have the technical term for it but you need not be concerned about the pressed in metal plates that hold trusses together. If you ever tried to take one apart you will be amazed at their strength. BTDT

I built my house and ordered 4/12 pitch 36' span trusses (for 2' spaced centers) from a truss company, viewed engineer certified drawings, built totally out of 2x4s with a double W per side. They had the over hang as I wanted eaves but not for ventilation as I blocked between them as mentioned herein.....ventilation was 4x12 pitched 12' vents on both end's.
Built the house in 1979 and have had zero roof/sheet rock problems with about 10 of bat insulation over most of the house, at least 3 1/2 at the edges.

Geo-TH,In · Nov 3, 2023

Before I can do anything, I have to get a permit and pass inspection.
Other than the cost for a permit, I have no issues getting an inspection.

BarnyardEngineering · Nov 3, 2023

East coast of North Carolina... Think HURRICANES. 150MPH of wind stresses a building far more than 150lbs of snow. Overhangs catch wind and peel rooves off buildings.

Janicholson · Nov 3, 2023

As important as the truss design is, and it should be engineered correctly, the critical ingredient is attaching the trusses to the sidewalls with hurricane strapping. shear bracing on the walls, and solid attachment of the metal to the trusses. These factors create a stable structure. Doubling fasteners at the roof edge and a minimum overhang (if any) assist in the wind resistance. Jim

MarkB_MI · Nov 3, 2023

> East coast of North Carolina... Think HURRICANES. 150MPH of wind stresses a building far more than 150lbs of snow. Overhangs catch wind and peel rooves off buildings.

My old beach cottage (which I sold back in the eighties) on Topsail Island has made it through multiple hurricanes despite having overhanging soffits. Proper attachment of the roof to the walls is essential.

Scott 730 · Nov 3, 2023

(quoted from post at 16:50:00 11/03/23)
Proper attachment of the roof to the walls is essential.

.............. as is attachment to the foundation.

Stephen Newell · Nov 3, 2023

On a metal building you don't have to frame an overhang, you can just let the tin overhang.

Roof Truss Design Help

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