Background: I am building an attached garage. I received bids from contractors and they were in the 60,000 - 90,000 range which is beyond my means so I decided to tackle the project myself. I have demolished the existing carport (flat tar and gravel roof) and have removed the exising badly cracked slab. The new slab will be poured this week. My questions are concerning the rafters and ceiling joists.

Garage size: 29'-8" deep by 25' wide
Roof slope: 3:12
roof loads in my zone: 20 psf live, 10 psf dead
existing house roof: 2 x 6 rafters/1 x6 plank decking, composition roof

My plans: Ceiling joists 2" x 12" douglas fir #2 spaning 25' (less 2 x 4 wall thickness)
The rafters will run perpendicular to the joists so I plan on 2 x 6 "strongbacks" 4' o.c. on top of the joists nailed to the rafters. I also plan on collar ties (upper 1/3 4' o.c.) Since the roof slope is 3:12 the first joist must be 4' from the wall edge.

Question # 1: Is it acceptable to place 2 x 6 "joists" from the exterior wall to the first joist 16" o.c.? (Span would be 4') Should I use joist hangers? Does the outside joist need to be doubled?

My plans: Use 2 x 6 (douglas fir #2) rafters to match existing roof. The existing roof uses purlins with the rafters 24 o.c. Since there are no walls in the garage I can not use purlins. The span is 14' - 10" and the way I read the span tables I need to space the rafters 12" o.c. I plan to cut the birds mouth 1/8" less than the existing rafters and use 5/8" rated sheathing for the roof decking.

Question #2: Is the above a resonable method?

I have decided to gable the roof over the garage since the angle cut on the joists would be severe for a 3:12 roof slope and the joist would only be 4" wide where it rests on the top plate. The existing roof is a hip roof. Is this a valid concern, or would a hip roof be acceptable even with the severe angle cut.

This job will be inspected but I haven't been able to contact the inspector to date so any comments will be aprreciated.

Way too many variables and questions for an answer or answers to be reasonably expected from a forum such as this. Retain an architect that knows what he or she is doing, and let him or her design a sensible logical simple structure for your garage. It is an approach such as yours which may have resulted in absurdly high bids. Whatever you pay a design professional will be saved many times over in construction costs.

This message has been edited. Last edited by: Richard Hetzel,

I'm a construction code official and construction inspector and I agree completely with Richard Hetzel.

What you have proposed, firstly, does not contain enough information to make any sensible conclusions...

And secondly, goes beyond the limits of prescriptive building code allowances.

From what you have explained, you need a design professional...an architect or engineer...to design this structure, and stamp the plans before you could even submit it for approval and get any permits from your local code office.

Originally posted by homebild:
I'm a building code official and construction inspector and I agree completely with Richard Hetzel.

What you have proposed, firstly, does not contain enough information to make any sensible structural conclusions...

Secondly,your proposed design goes well beyond the limits of any prescriptive building code allowances.

What this means and from what you have explained, you need a design professional...(an architect or engineer)...to design this structure, and stamp the plans before you could even submit it for approval to get any permits from your local code office.

Thanks for the responses, I will take your advice and contact a design pro. I agree the stamp would aid in the inspection process. There will be 2 foundation inspections (pre and post concrete pour), plumbing, electrical, framing and final.

I am not sure why the bids came in so high but I have a good idea as to why. Based on my material take-off, the signed contracts I have with the concrete contractor, licensed plumber, licensed electrician and roofing contractor and adding a contigency amount the cost of the garage will be about $22,000. The work I perform: demolishing the existing carport/workshop with a tar & gravel roof (done), removing the existing slab (done), framing and finish carpentry certainly does not make up the difference in the cost of the bids.

I have looked into using trusses for the roof and the cost is actually cheaper than stick building the roof. The problem is getting the trusses delivered to the site. The closest the truck can get to the site is 2,000 ft. I am concerned about getting a concrete truck to the site. The only issue I had getting a building permit was road frontage. City code requies a 50 ft. frontage to a road for a building permit and I have 12 ft., the width of a winding dirt road that dead ends at my property. The house was built 42 years ago and I have lived here 25 years. I ultimately had to go to court house and find the documents where the city was granted ownership of the dirt road to get the permit.

With the exception of running the ceiling joists perpendicular to the rafters, the framing is standard framing and the tie in to the existing roof is quite simple and fixes an existing problem, a sagging hip rafter. The reason for the 29' - 8" depth is so the door from the house will open into the garage.

One more question: Should I contact an architect or structural engineer?