Loft Conversion Joist Troubles

Postby Matt Damon » Mon Mar 23, 2009 10:42 am

Hi everyone,
Hope ive posted this correctly as im new to the whole FORUM thing...
I am having a few concerns with a loft conversion i am undertaking.
I have had the Joists sized by a structural engineer @ 9 inch * 2 so im happy with that part.
The issues are as follows.
1. The amount of the Joist i am cutting back to get the timber to sit under the apex and sit on the existing pan, means that there is probably only 2 rising to 5 inches sat on the 4 inch Pan is this strong enough?
2. i have packed the Wall Pans off by 1 inch as to raise the new (independant) Joists from the existing ceiling but the centre pan is 30 mm higher than the 2 no. outside walls. So do i :
a) Raise the pans on the outside walls to level up (didnt like this as it will reduce the timber profile again.
b) Run down the underside of the Joist with a circular saw to level up ?

Any advise would be appreciated.
Matt Damon
Posts: 2
Joined: Mon Mar 23, 2009 10:16 am


Simply Build It

Postby Dibble » Tue Mar 24, 2009 3:13 pm

I am in the process of a similar job. I started by visiting the local council building control where I received a very handy pack plus cd with loads of usefull stuff on. I may be wrong, but if you wish to class the conversion as habitable space, eg a bedroom, you will need building regulations approval. You don't need to submit plans but you do get site visits and good advice whenever needed. Looking at my span table, 220x47 joists at 400mm centres will span up to 4.58 metres. You could use 195x75 instead and save an inch on height.
Posts: 11
Joined: Tue Mar 17, 2009 3:17 pm

Postby Matt Damon » Fri Apr 03, 2009 3:40 pm

Many thanks for the response. Yes you are quite correct and i have submitted a Building Regulation Application @ a hideous cost...
The Timbers unfortunatley require this size as one of the spans is app 5mtr.
I have now sorted the level issue by adding a splice to the offending timbers..
Next question does anyone know of a rule of thumb or sizing chart for trimming the loft.. as the stairs run across the line of the timbers i will need to trim 7 no. ceiling joist- and then add the new larger floor timbers.
I was going to trim by bolting 2no. 9"*2 timbers together and using this as the trimmer - fix byusing a wall-timber hanger and then hang each individual timber(Ceiling and floor joist) onto the doubled up joist.

Thanks again + keep me posted on yours Dibble :D
Matt Damon
Posts: 2
Joined: Mon Mar 23, 2009 10:16 am

Postby Dibble » Sat Apr 18, 2009 7:44 am

As you have paid for building regs. make use of them by asking advice and if necessay getting a site visit. I received a pack from my local building control office which included a cd rom with loads of useful stuff on. I'm sure it included a chart on trimmers.
Posts: 11
Joined: Tue Mar 17, 2009 3:17 pm

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