Long/reinforced roof joist options

Joined
17 May 2013
Messages
1,370
Reaction score
26
Country
United Kingdom
*Updated with elevations, etc*

Here are some plans of our log cabin. These are updated versions from the ones we signed off on and we noticed in the very middle they have specified the joist as two pieces, joined under the ridge and braced with an upright which was not there previously. You'll see that rather than using trusses, the roof is designed to be supported on the walls which are built all the way up to the ridge.
You'll see 'notches' in the elevations A-E for these roof beams. I believe they are quite a heavy spec, like 4x2 or even 6x2 presumably to make up for the relatively large joist spacing.

If you look at elevations 3 and C (and to an extent D) you'll see they have 'partitions' at the top, like these were solid walls and they've cut holes in them. We believe this is because our cabin is a bespoke variant on an existing design which did have those walls.

I can see based on this design that the upright is an easy 'fix' but it was not in the design we gave them, or their plans which we signed off on - and it's quite impactful on the overall design.

What I'm wondering is if we can relatively easily avoid the need for this upright - with a long very strong joist basically. If this could be 'dropped in' then great.

Another thing I'm interested in is those 'partitions', especially the one along the cabin (wall 3) - if it is serving a major structural purpose or not.

upload_2019-10-14_12-58-56.png

upload_2019-10-14_13-0-13.png

upload_2019-10-14_13-0-33.png

upload_2019-10-14_13-0-58.png

upload_2019-10-14_13-1-18.png

upload_2019-10-14_13-1-55.png


upload_2019-10-14_13-2-25.png

upload_2019-10-14_13-2-47.png

upload_2019-10-14_13-3-7.png
 
Last edited:
Sponsored Links
I suppose I was thinking more about engineered beams etc though this is interesting to look into as well. Obviously an RSJ would work but that might be overkill.
Any guesstimates on costing anything like this or where to buy appreciated; it would have to be delivered.
 
We spanned over 7m using Posi-Joists by Trussform. They were pretty meaty fellas at nearly 450mm deep and 120mm wide. On the plus side, it is difficult to miss a chord when fixing plasterboards!:mrgreen:
 
Sponsored Links
Im not sure if the upright is going in the loft or in the room.

In general yes you can get beams 6m long, solid timber is available upto around 7.2m

Glulam beams are readily available lengths off the shelf upto 11metres, I used to buy from glulambeams in Southampton.

Prices are typically around £700 per cubic metre. So a 315mm x 90mm would cost £20 per metre exc vat.
Delivery is expensive though.
http://glulambeams.co.uk
 
Why do you not want hangers in the middle of the roof? Is this loft to be used for storage, or is it to be for habitable use?
To use posi-joists if you are not using the roof space would be expensive.
 
Why do you not want hangers in the middle of the roof? Is this loft to be used for storage, or is it to be for habitable use?
To use posi-joists if you are not using the roof space would be expensive.
When you say hangers, do you mean a vertical from the ridge?

I think I'll need to post some plans but for now note I said the triangle is filled in, it's not using a typical truss design.

There are effectively 5 'trusses' on an 11.5m length roof and all but this one right in the middle are designed to fit over load bearing walls.
Do to keep the same principle they put a pillar in the plans and didn't mention it. So we're looking to retroactively sort this without changing the main design which is already in construction.

It'll make more sense when I get access to my pc and can post plans
 
When you say hangers, do you mean a vertical from the ridge?

I think I'll need to post some plans but for now note I said the triangle is filled in, it's not using a typical truss design.

There are effectively 5 'trusses' on an 11.5m length roof and all but this one right in the middle are designed to fit over load bearing walls.
Do to keep the same principle they put a pillar in the plans and didn't mention it. So we're looking to retroactively sort this without changing the main design which is already in construction.

It'll make more sense when I get access to my pc and can post plans

Im sure you could replace the joined joists with something self supporting.
As its under building regs you would need a calc done though.

If there is just a loft void then you might be able to put in a double or triple joist or a glulam.
I once did a suspended floor in timber joists with a clear span of 5.5m. From memory the joists were 12 x 2 or 12 x 2.5, but obv that was for a domestic floor load.
 
Im sure you could replace the joined joists with something self supporting.
As its under building regs you would need a calc done though.
I was wondering about regs. What do they require to be satisfied in terms of structural requirements in a fairly simple building? Full calculations for every wall and joist and beam or only where there is doubt?
Because this is a prefabricated (but self assembly) building we know the manufacturer has done required engineering but not exactly in what manner. We expect BC to put questions to us which we'll pass on.

Hence the desire to make minimal changes only.
 
With the size i take it the cabin not cheap. If not already purchased/paid for i'd be inclinced to find a supplier who will meet your needs not you meeting theirs.
 
It's a bespoke cabin designed to our plans. But they omitted the post in their official plans sent for approval, and we think only added them in their final version once it went to manufacturing.

Seems most likely it was always supposed to be in their design but we never saw it when we approved the plans.
It's a bit late in the day now, given a 14 week lead time, as we cannot really afford to delay. We're chasing them to address it but I want to look into all options since time is to an extent more valuable than money and if there was a quick fix on our side we might just do that and try to get some reduction on overall cost
 
Right. Most probably thier cheeky error. If concealed in the ceiling void you could go for the following type joists. but they will need to be fixed to the outer wall. That then adds issues due to the load bearing now shared only be two walls instead of two walls and a support colomun inside.

https://www.merronbrook.co.uk/easi-joist/ Span table on page too.

A trussed roof maybe an option too but it's the cost of the redesign.

Before you start shelling out extra cash i'd ask to see the set of plans you signed off. If you have signed for no supports i'd be asking for the cost of the retrofit by you to be deducted.

Is the log cabin insulated single wall one.
 
Good advice, thanks.

That could be an option, at the very least it's interesting to see what is out there. I'll put up some specs tomorrow exactly what we have.

I know mistakes happen, even with an architect engaged sometimes. It's how they are dealt with that's important imo
 
yes i agree. Be nice to see the spec. If they turn out to be helpful it should be a breeze to get done.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top