New workshop build - structural questions

[Joe Shmoe]

Hi Folks

Looking for some advice on my impending workshop build.

3.5m wide by 5m long.
Cement based cladding (Eternit or Cedral) with (most likely) an artifical slate tile roof covering.
Framed with 4x2, and using 6x2 for all rafters and raised chords, and 8x2 for the ridge board. Uprights and rafters every 400mm or so.

Ive attached some sketchup pics, but note that I've left off some rafters and chords for clarity as its hard to see otherwise.

Questions.

1) I've constructed previous builds using trusses with ply gussets. This is my first time using a ridge board approach. I wont be using the loft space for any storage.

a) Is a 27degree pitch favourable, will it be walkable with artifical slate?
b) Is 2x8 suitable sizing for a ridge?
c) Is 2x6 suitable for the rafters? Width of workshop is 3.5m.
d) Could the raised chords be reduced from 6x2 to 4x2 ?


2) Ive left a 2m gap for some double doors but am concerned about a lack of support for the roof in that section. Ive doubled up on the wall plates. Any view?

Thanks in advance for highlighting any design issues.

 

[RobinBHM]

The sections seem to be about right.
4 x 2 should be fine for a collar as it is acting in compression.

6 x 2 should be plenty strong enough for common rafters.

If you are using breathable membrane and insulation, tyvek, kingspan and marley all have useful downloads showing sectional details. The outside cladding needs a 25mm cavity behind it, vented at the bottom.

Tyvek show quite a few options for insulating between or above rafters.

Your roof design will be strong enough to walk on, not sure about artificial slate though.

 

[blackrodd]

Drawings look OK. The ridge is usually 6", or 7"x 1 1/2" but 2" will be OK
It's good practice to keep the studs at the same centres as the rafters and doubleing the head , or wall plate.
I've erected and worked on quite a few timber framed houses, and favour copying their wall and panel arrangements.
Any concerns about the entrance door could be addressed above by filling in all of the end of the gable truss/rafters
making it really strong, incorporating the double head you proposed.
Two rows of the dreaded noggins through the studs will make a stronger job too!
Don't forget the binders and wind braces in the roof area. Googling should tell you all.
HTH Regards Rodders

 

[mindthatwhatouch]

Could always put a single wall plate if each rafter is above an upright stud.

Two 4 x 2 (or 6x 2) on edge on top of the wall plate across the doorway would suffice.

Have you looked at Metrotile or Decra for the roofing?

 

[Phil Pascoe]

"I won't be using the loft space for any storage."
=D> The old ones are the best ...

 

[Joe Shmoe]

Hi. Works have started. I went for a 7x2ridge and 6x2 rafters.

Before I start cutting them all, anyone see any issues I should address first?

Question. How should I fix the rafters? At the ridge end, do I nail directly through the ridge with two nails for the first, and then scew nail for the one the other side?

How do I fix it down at the wallplate?

 

[blackrodd]

I've answered this on you're other roofing post.
The link below will answer you're question, cut a complete pattern and use that to mark all the rest

Nail/screw through the rafter at the top into the ridge board, and skew nail/screw two each side,
Fix the truss clips, as directedat the seat cut, at the birds mouth, on the wall plate.

https://www.google.co.uk/search?q=rafte ... L5X3nNw%3D

http://www.tradefixdirect.com/builders- ... AtU_8P8HAQ
Regards Rodders

 

[Joe Shmoe]

Thanks for the tips Rod. All done as recommend.

Can anyone advise why my gable end ladders are pulling down with the weight. Have I constructed it incorrectly, or will a eaves facia help stop it sagging?

 

[HOJ]

Not sure I would put a ladder on the gables on a timber frame, just finish at the end rafter with an over hang on the roof.
In your case the ladder should be set back from the gable wall line and the wall built up underneath to support it.

 

[blackrodd]

Not sure I would put a ladder on the gables on a timber frame, just finish at the end rafter with an over hang on the roof.
In your case the ladder should be set back from the gable wall line and the wall built up underneath to support it.

I would think that a ladder truss on the gables and a wide soffit and roof overhang is good for a timber building,
It's helping to keep the worst inclement weather off the walls etc.
Regards Rodders

 

[Rottie Mad]

I'm not really in a position to comment as I'm currently in the design phase of my own workshop and have a WIP thread I started creating today with some structural questions of my own.

However with that said, if I were in your shoes.......... I would turn your one ladder into say 2 smaller ladders on the end.

I think this would help with the sagging........... Once sheathed with OSB or similar and battened the roof overhang will be well supported imo

Liking your work so far along with attention to detail I have found your thread very informative and thorough so far......... Keep up the good work

Hope this helps

RM

 

[paulrockliffe]

Extend the ladder to the next truss inwards and it'll sort that out won't it? At the moment most of the weight of the lader is hanging over thin air and unsupported and it's trying to rotate the ladder around the support posts and down onto the ground. If you tie to the next truss as well that will give you some leverage to resist the forces on the overhang as you'll create a much stronger cantilever.

 

[Paul200]

Like this....

Cheers

Paul

 

[Joe Shmoe]

Great, cheers guys, makes sense.

I didn't want to rebuild the whole lot so just added some noggins yesterday to tie the ladder to the previous rafter and that tightened everything up. I'll know for next time.