Strengthening Loft Floor

[Dankly]

Hi all,

I am at the planning stage for a loft conversion in my 1950's 3 bed semi. It will eventually consist of a hip to gable roof with full width rear dormer, but I will be doing most of the work myself and so will be doing it in stages to keep costs and disruption to a minimum.

First job is to reinforce the floor (to building regs), with all future loadings considered at this point (dormer, internal walls etc). I'm not looking for anyone to give me calcs and will of course be enlisting a SE in due course, but before I do so I'd like to put the feelers out to get a general idea whether I'm in the ballpark or barking up the wrong tree.
I'd ideally like to work with flitched beams where possible due to the fact that I'll be doing the majority myself and need to keep things manageable (lightweight). I also have restricted headroom and will need to keep timber/beams to as shallow a profile as possible, with 170mm being the absolute max. I know people say it's better to have a gap between ceiling joists and new floor joists but I simply couldn't do it as it would make the height unworkable, so I will be looking to cut through the ceiling joists (after temporarily supporting) and then fixing them to the new joists.

Picture 1 is the layout as it is. Not shown is the roof structure, which is currently supported midway down trusses with 9x3 purlins sitting on the load bearing walls. I would ideally like to remove those purlins as part of the roof phase (the rear will be a dormer anyway, and the right hand side will be a gable) and building a supporting stud wall in its place so the roof will be supported from this wall built on the new floor/joists instead.

Picture 2 is a rough idea of how I see it potentially working with flitched beams, using span calculators and a bit of guess work. The trimmer/trimming joists are where it could maybe not work out, but then I'd also be willing to add a second steel plate to any beams that fall below regulations. If I absolutely have to use steel beams then I will do, but really want to try to avoid it if possible. I'm not in a rush and understand that it'll be more work using flitched beams. FYI, the joists in the top right corner of the image are running vertically due to the route of future soil pipe.

Any insight/opinions/ideas would be greatly appreciated, and if I need to provide any further info please let me know. Thanks.

Dan

 

[old duffer]

its like asking the internet what could be wrong with you before you go the the doctors....just ask the SE silly....

 

[Murdochcat]

1. Architect
2. Planning Permission
3. Structural Engineer
4. Party Wall Surveyor
5. Building control

Before you do anything?

Or you could end up in the mess outlined on this forum the other day .........

And probably speak to your neighbour as you might need their cooperation for access / scaffolding too

 

[Dankly]

1. Architect
2. Planning Permission
3. Structural Engineer
4. Party Wall Surveyor
5. Building control

Before you do anything?

Or you could end up in the mess outlined on this forum the other day .........

And probably speak to your neighbour as you might need their cooperation for access / scaffolding too

1. Why?
2. Not required as it’s permitted development.
3. I’ve said I will be enlisting a SE.
4. Of course, once I actually have a plan.
5. See 4.

I’m at the planning stage. I’m merely looking for information from people in the know or who have done something similar. Or who wanted to do something similar but couldn’t for whatever reason. That’s what this forum exists for, no?

 

[freddiemercurystwin]

You need to know how the roof will work structurally, the floor upgrades and the roof structure changes are often interlinked. For example it's quite common for steels to be inserted beneath existing purlins with stud walls built up under the purlins, then the roof structure inside the roof void can be chopped out, then the steel beams carry the new floor.

 

[cdbe]

The random arrangement of flitch beams just confused me, the spans aren't great so the steels won't be unmanageable (I put all mine in pretty much singlehandedly), an SE will probably have to design (£££) the flitch beams in addition to the load calculations instead of just selecting "off the shelf" steels.

Have you looked at lowering bedroom ceilings to create headroom - not that difficult. Also, there is a government consultation at the moment considering increasing PD allowances - there is mention of raising ridge heights to allow headroom so it could impact on future works - although any gain will need to be offset by more onerous insulation requirements.

I've done the back to front loft conversion myself (built half of it before any structural calculations etc and it was a nightmare).

I would take your sketch, remove all those joists and beams, add in your dormer, internal walls and any bathroom etc then get an SE in with the brief that you want maximum headroom and voice your concerns about the steels and your interest in flitch beams (but I suspect they might need to be taller than equivalent steel and thus compromise your headroom again).

 

[Murdochcat]

1. Why?
2. Not required as it’s permitted development.
3. I’ve said I will be enlisting a SE.
4. Of course, once I actually have a plan.
5. See 4.

I’m at the planning stage. I’m merely looking for information from people in the know or who have done something similar. Or who wanted to do something similar but couldn’t for whatever reason. That’s what this forum exists for, no?

Have you checked that PD is allowed in your area?

 

[Dankly]

You need to know how the roof will work structurally, the floor upgrades and the roof structure changes are often interlinked. For example it's quite common for steels to be inserted beneath existing purlins with stud walls built up under the purlins, then the roof structure inside the roof void can be chopped out, then the steel beams carry the new floor.

Thanks. Yes I know I may well need a beam underneath the purlin or new roof support. Those outermost flitched beams are around the location of the purlins and so could serve that purpose, whether they end up as flitched or steel.

The random arrangement of flitch beams just confused me, the spans aren't great so the steels won't be unmanageable (I put all mine in pretty much singlehandedly), an SE will probably have to design (£££) the flitch beams in addition to the load calculations instead of just selecting "off the shelf" steels.

Have you looked at lowering bedroom ceilings to create headroom - not that difficult. Also, there is a government consultation at the moment considering increasing PD allowances - there is mention of raising ridge heights to allow headroom so it could impact on future works - although any gain will need to be offset by more onerous insulation requirements.

I've done the back to front loft conversion myself (built half of it before any structural calculations etc and it was a nightmare).

I would take your sketch, remove all those joists and beams, add in your dormer, internal walls and any bathroom etc then get an SE in with the brief that you want maximum headroom and voice your concerns about the steels and your interest in flitch beams (but I suspect they might need to be taller than equivalent steel and thus compromise your headroom again).

Thanks for the constructive comments. The reason I've drawn it the way I have is essentially to make use of the load bearing walls, also to trim round the staircase opening, and also to keep joist spans as short as possible to allow for shallower timber. I agree that it's going to be more costly doing it this way in terms of plans and probably even materials.

I don't fancy lowering the ceilings as they are already 100mm lower upstairs than down. I don't mind having limited headroom in the loft as long as its practical, and I think I can squeeze it in. I'll definitely look into that consultation, mind.

I'm not planning to do anything back to front. I won't be doing any work at all until I've got SE calcs, I just want to brainstorm a bit first to make sure I don't forget anything or get caught out .

Good advice, cheers. Can I ask what size steel and span you used for your floor please? Just for an idea of the size/weight etc

Have you checked that PD is allowed in your area?

Yes it is.