Multiple Timbers on wall top plate

[SilverSaloon]

Hi

I am looking at an loft conversion.

Currently my ceiling joists are fixed to the rafters just under 200mm up from the wall plate.

The wall is a very thick old stone wall. The rafters sit on the outer side of the thick wall leaving the inner side free/clear

I am putting 200mm joists in spanning the room, but need to know if i can simply pack the gap between the top of the wall to the bottom of the new joist (and ceiling jost for that matter) with several lengths of timber?

My plan was to put 3 lengths of timber (45mm high) along the top of the wall bedded in with mortar and then the joist screwed to this. With a final smaller piece of timber (about 30mm high and probably about 40mm across) to accurately level the new joist.

Is there any flaws in this idea? Any other ideas? I could lay a course of breeze blocks along too with x2 lengths of timber on top but that would be tricky as the existing rafter means they are just slightly too wide so would require a lot of time to modify before laying so they clear the rafters. I can do this, but timber seems a quicker solution....

thanks for any advice, suggestions.

 

[ree]

At first glance i would say no. But i dont really understand your post. Could you post pics, and a sketch of what you propose?

Joist sections depend on span dimensions.

 

[SilverSaloon]

Attached is a quick diagram of what I mean

To the left is how it is now.

To the right is what I want to do - add a 200mm joist for the new floor. As this needs to rest on the wall and the current ceiling joist doesnt, can i "build up" the wallplate to meet the joist.

The blue could be a course of bricks i guess, and then the green could be a timber length. Or could it all be timber? The yellow box is the new 200mm joist next to the old ceiling joist.

Span is about 3 metres then there is a load bearing wall

Untitled

• SilverSaloon
• 20 Jan 2015
• 1

 

[noseall]

That looks fine and is a typical wall plate/rafter/joist section on any modern build (without the cavity of course!).

 

[SilverSaloon]

even building it up in wood rather than brick?

 

[ree]

You show, essentially, a double wall plate (in wood is fine) thats best bolted, or anchored, into the wall. Clipping and/or bolting the old joist and the new joist and the rafter together and pinning them to the plates would be best Rolls Royce practice.

AAMOI: How come you dont show a wall plate with the rafter bird's mouthed to it? Is the guttering on rafter straps?

 

[noseall]

even building it up in wood rather than brick?

Wood will be ok.

The benefit of laying a masonry course is that you have the opportunity to level/straighten things up a bit prior to bedding the plate.

If you are butting you new plate up to the existing rafters then you may need to retro' fit some truss clips to the end of each rafter where it abuts the plate.

Don't forget bent holding down straps every 2m on the plate.

 

[SilverSaloon]

thanks for all the advice.

As I will be using 50mm timber strips (in height) i would need to have 3 of these ontop of each other and then one final one that will be of various sizes 50mm or under to level the new joists.

The current rafters sit on a ~20mm wall plate on the outer side of the top of the wall.

The guttering is cast iron and is attached via a metal bracket that screws to the top of each rafter end. The cottage is 170 years old, although the current roof rafters etc I suspect has been replaced sometime in the 1900's as they look too new to be the originals.

 

[ree]

What section size, & what length, will be the proposed "timber strips"?
Given the accessability, & with help, you could struggle a heavier section wall plate, or double plate, up there?



Just saying FWIW, given your aim is a loft conversion a couple of things:

Why not pin lookouts to the bottom of the rafters:
this will enable a soffit and fascia and the possibility of easily renewing the guttering.
The projection also keeps any damp away from the wall plates.
When exposing the rafter tails you will be able to check them for rot.

I wouldn't be too convinced about the present in-place 20mm wall plate - it could be that all you can see is the top 20mm of the plate. But, anyhow, what condition is that plate in?

Any work interior or outside should be done from at least a tower/platform.

 

[SilverSaloon]

I dont really want to create soffits as it would take away the peroid look of the cottage on the outside, and would be extra work too. Quite like the look of how it is now.

The timbers i planned to use were 4.8 meteres long, staggered across the whole house where they join. 2x 120mm x 50mm and onto of that 2x 100mmx50mm (as the rafters start to hit 120mm here so would either need to cut a birdmouth in the rafter or fit thinner wood. Its also worth noting that i plan to tie this into an internal stud frame arrangement that i will be adding to insulate the rooms inside, effectively creating a small cavity inbetween the old stone wall and the insulated studwork. This will be a structual stud wall too up to the joist height.

The existing thin top plate is okay and so are the rafter ends. As I say the roof woodwork is fairly recent compared with the age of the cottage. The barn next door that has original roof on is rotted and will need to be replaced soon

 

[ree]

Fair enough - it was simply a ball in the air.

Sounds good - thing is, you are not looking for pure support but support and well tied-in components.
Just tie the insulating frame into the rafters - the top plate can be rafter angled or flat.