Portal frame garden room / garage

[Clive67]

I am planning a multi purpose garage / workshop / garden room for my back garden, I want to stay within permitted development guidelines of 2.5m to the eaves and 4m height overall, and in addition to keep it to <30 square metres to avoid building regs.

 

I have seen some very interesting use of timber I beams / joists to create portal frames, this is really appealing to keep the interior as uninterrupted as possible and I assume is fairly cost effective.

 

Can anyone recommend a structural engineer who can spec a portal frame of this construction please?

[George]

For a small structure it'd probably be easier to have a normal building but instead of roof trusses, use a ridge beam and single spanning rafters to get the vaulted ceiling. There are a few structural design features that should be employed for vaulted ceilings, e.g. plywood sheathing, stiffness of the ridge beam, lateral stability,rigid rafter connections... but is easier to build than a portal. If you really want a portal, I would approach timber frame manufacturers direct in case they have a more standard design.

 

Avoiding building regs shouldn't be your primary motivation for sizing. If you want to use it as a habitable (i.e. heated) space, you'd be hitting BR requirements anyway.

 

Anyway, whereabouts in the country are you.

[Bozza]

52 minutes ago, Clive67 said:

I am planning a multi purpose garage / workshop / garden room for my back garden, I want to stay within permitted development guidelines of 2.5m to the eaves and 4m height overall, and in addition to keep it to <30 square metres to avoid building regs.

 

I have seen some very interesting use of timber I beams / joists to create portal frames, this is really appealing to keep the interior as uninterrupted as possible and I assume is fairly cost effective.

 

Can anyone recommend a structural engineer who can spec a portal frame of this construction please?

This is so weird.  This is exactly what I’ve been planning for a while now, and have looked at both steel frame structures as well as timber ones.   8x4m and to maximise height to 4m also to keep within planning regs.   Ultimately I’ve decided to go for a more traditional timber framed structure and today have taken delivery of a stack of 4x2, to build it myself.    The steel building companies will happily quote, and they do the required engineering calculations.

 

I have ended up with a quantity of box steel (long story) so my intention is to self build my structure with the 4x2, reinforced with the steel, steel roof with larch cladding and properly insulated etc.    Just undecided about the foundation system.  
 

like I said I got quotes for portal steel frames with a view to in filling with timber, using the steel to take the load.

[Clive67]

Thanks George, that approach was my default option but I was intrigued by the portal frame concept as it looks very elegant, and if it's timber it's easier to work with than steel.

 

I would like bifold doors across one end and wasn't sure about taking the load from a ridge beam vertically down to the middle of a steel header above the bifold opening. I think it would be better to take the load to the outer corners which obviously a portal does naturally.

 

The shape and style of building would be quite similar to this:

 

https://www.wydertimber.co.uk/my-product/northstone-feature-marketing-huddle/

 

I contacted Wyder but I am out of their region (I'm in Warwickshire).

 

I did look at steel buildings but they seem quite expensive for what they are? And often ugly!

 

The site is quite constrained so keeping it to 30m2 is as much to do with that as removing the need for regs.

 

I want to be able to get a Defender in there so I need to maximise the entrance height, 2.1m ideally.

 

All I really need to know is:

- what size of I beam and material spec eg OSB etc

- what centre spacing

- what material and orientation for the joint bracing and spec of glue to get the required strength

 

If a timber supplier can precision cut the beams to the right angles then it's a lovely kit of parts to glue together and erect.

 

 

[Clive67]

Bozza - sounds like you're a few steps ahead of me! Good luck! What foundation options are you thinking of?

[Bozza]

13 hours ago, Clive67 said:

Bozza - sounds like you're a few steps ahead of me! Good luck! What foundation options are you thinking of?

Ok so option 1 is numerous m24 threaded bolts cemented into post holes, with treated timber bolted onto the rods.

option 2 is to build several cement pillars with treated timber across.  Option 3 is a strip foundation cement and bricks/blocks.  All would work just unsure which system, pros & cons to all.

Edited May 22, 2021 by Bozza