Adding a floor to a loft

[mhuk]

I've lurked here for a long time but now is the time to ask a question

I tried "search" but couldn't find an answer so apologies if you see this question every other week.

I'd like to add a proper floor to the loft in my Edwardian mid-terrace house (a non-habitable loft space with a wooden loft ladder for access); the approx floor size is 18 x 18 feet. The photo below shows one of the four ceiling binder on top of the ceiling joists: one under each eaves end and two equi-distant in the middle of the floor space:

There is load-bearing wall in the middle of the loft space, that runs parallel to the purlins; on the ground floor it is two bricks wide but on the first floor it is only 1 brick wide. There is also a "proper" load bearing wall (the top of outside wall of the house) 4 feet from the end of the loft space.

The initial idea was to run floor joists parallel to the existing ceiling joists with the ends resting on the wall plates but I can see no way of running floor joists like that as the ceiling binders are in the way.

The other option that sprang to mind is to attach 7x2" (or similar) to the walls at each end of the loft space and using hangers run larger binders parallel to the existing binders, so the top of the new binder is higher than the top of the exisitng ceiling binders and so that there is a 1" between the bottom of the new binder and the ceiling joists (to prevent them from bearing down on the ceiling if the new binders flex). The number of new binders would be determined by tables.

I would then run floor joists across the new binders, parallel to but not touching the ceiling joists, with a binder as close to the each of the joist to act as a pseudo wall-plate (although the space between the purlin and eaves will be used for light storage so there would be much additional weight on the ends of the joists.)

Hope you're still with me

Given the width of the loft space (the width and length is about 18ft) this would require each new binder to be joined in the middle, as would the new floor joists, using the method show in the photo below :

An alternative might be to use I-joists (has anyone used them for this purpose and are they expensive?), although I don't think a crane could reach the house my front garden is about 6m and there are telephone cables in the way (if I were to get them craned in when I get the roof done):

Hopefully that made sense. Am I on the right track or is it not possible? Is there a better way to do it? I'm not planning on making a habitable room (I can't afford to get a staircase and dormer fitted) but I'd like the floor to comply with building regs if at all possible (even if I don't apply for them). Will the floor need Building Approval?

Ideas and suggestions very welcome

 

[mhuk]

Many thanks for moving it

 

[Shytalkz]

If you're just going to install the new joists and leave the existing purlin props as-is, prop the existing joists from below and remove the binder. Install 50x175C24s alongside each ceiling joist, spanning between the front/rear walls and the central spine wall (they can joint over the spine wall) set 10mm above the existing ceiling level and nail the existing to the new along the length. In this way, the ceiling is now supported by the joists and you don't need a binder. The joists will need to be chamfered at the eaves end, else they'll poke out of the roof .

As you'll have a hallway adjacent to one of the party walls, there will be no support (well there will, but it will be insufficient) to the new joists on that line. So, assuming that the existing joists are 3x2, notch the top of them by 25mm and install 2/50x100C24s nailed together, set so that the top of these is flush with the top of the new joists and support the new joists with hangers. You will need to timber pack at the support position on the spine wall with timber up to the underside of the joists; at the other end, put them into joist hangers cut into the party wall. Technically you need a Party Wall etc Act agreement to do this.

If you want to build stud walls and lose the purlins and props, change the joist sizes to 75x175C24, build a stud wall off these new joists just behind the purlin position using 50x100C16s at 400, with 100x50C16 sole and headplates; notch the underside of the existing rafters to get a square seating on top of the studwork. Do not remove the purlins and props until this wall is complete.

If you want to continue and make it into a pukka habitable room complying with BRegs and insulate, then put an additional 50x100C24 alongside every rafter, from the ridge board to the studwork, birdsmouthing over the stud.

Note, if you don't have a fixed stairs, then it doesn't have to comply with BRegs in terms of MoE windows, thermal etc; as long as Part A is satisfied, ie structural, then you'll be ok. If you leave the existing purlins and props in, then you're not really changing anything structural, so no BRegs; if you remove them, then this is a structural alteration, so you will need calculations in support and BRegs appro (although there are many who don't bother with that...).

Don't use TJI joists: too fiddly and there's no need to anyhow.

HTH

 

[mhuk]

Many thanks for the detailed reply

I'll need to re-read a few more times but you mention purlin props; there are no props per se although 12 feet the other way from the photo, the external wall supports one purlin (looks a 2 brick x 2 brick column) and the end of the loft space passed the brick purlin support is the bit of the bathroom that is over an alleyway. I don't plan to remove the purlins - I'll build a simple stud wall below the purlin and add cupboard doors (also plan to insulate and plasterboard it but haven't got that far yet).

I don't quite understand the "hallway adjacent to one of the party walls" part: yes there is a hall under part of the floor space. This is the hall above and below:

Could you explain it in relation to the photos; is the loft hatch a weak spot? Would your method meet building regs?

Would the additional 50x100C24 alongside every rafter be attached to the existing rafters in any way?

Thanks again for your help- much appreciated.

 

[Shytalkz]

If you go to my profile, my email is on there; scan and send me a quick sketch layout of the first floor, with approx dims and the relative position of the purlins dotted on and I'll email back with the info overlaid. A picture paints a thousand words and all that...

 

[mhuk]

Mant thanks for the offer, I'll do it after I've been to the tip.

Three other things I've been pondering (although the floor is the main point):

1. Do "standard" Velux loft windows meet the the Fire and Thermal Insulation parts of Building Control for lofts? Is there a minimum width or do they have to specifically be purchased as MOE windows?

2. Looking at the photo of my hall and the photo below (not mine):

would it meet regs if it were enclosed and had a firedoor fitted, in the same position as shown but with a differnt last dog-leg? Would having the last dog-leg to the left or no last dog-leg have the least impact in the room on the left of the hall (bathroom)? Do 600mm width stairs meet Building Regs?

3. If something simialr to those stairs (but meeting the Fire regs) were suitable, can I move the doorways and create new ones under the same Building Control process if I went the full monty?

 

[Shytalkz]

1. Do "standard" Velux loft windows meet the the Fire and Thermal Insulation parts of Building Control for lofts? Is there a minimum width or do they have to specifically be purchased as MOE windows?

2. Looking at the photo of my hall and the photo below (not mine):

would it meet regs if it were enclosed and had a firedoor fitted, in the same position as shown but with a differnt last dog-leg? Would having the last dog-leg to the left or no last dog-leg have the least impact in the room on the left of the hall (bathroom)? Do 600mm width stairs meet Building Regs?

3. If something simialr to those stairs (but meeting the Fire regs) were suitable, can I move the doorways and create new ones under the same Building Control process if I went the full monty?

1 No, you have to get specific MoE top hung Velux, which comply with min opening area of 0.33m2, with min dim in either direction of 450mm. They have to be sited with the bottom min 600mm max 1100mm above finished floor level - that invariably means the purlin is in the way, as the window will cut across it.

2 You could enclose it at the bottom to form the requisite protected shaft, but the door can't be directly next to the tread: it has to be min stairs width away from the last nosing, or, if opening into the stairs, stair width + 400mm. Same applies if you do it at the top, within the loft, but you wouldn't have to enclose the stairs down to first floor level.

3 It used to be that you had to upgrade any doors from existing habitable rooms that opened onto the stairwell at first and ground, by means of perco self-closers. I believe that's been relaxed slightly now, but am not 100% sure as to what exactly is required these days tbh. Woody, can you advise on this?

 

[mhuk]

I think I'll just concentrate on getting the floor right and think about the rest at a much later date. I also got the size wrong, it's 8m x 5.55m.

shy: diagram emailed.

 

[^woody^]

Loft conversion have to rely on a protected escape route down the stairs/landing, and not via the windows anymore - so dimensions ans siting are irrelevant now.

Stairs should have a landing top and bottom at least as long as the stairs are wide

Don't forget that you will need 100mm rockwool suspended on chicken wire between the floor joists

 

[mhuk]

Thanks for the info

Would they still need to be MOE loft windows or can I use my current Velux loft windows, which are roughly 700 x 1100?

It's a real bonus if I don't have to remove one of the purlins and makes it far more tempting to go for full BR (not sure if that's a good or a bad thing!). Do you have a link?

 

[Shytalkz]

Loft conversion have to rely on a protected escape route down the stairs/landing, and not via the windows anymore - so dimensions ans siting are irrelevant now.

Stairs should have a landing top and bottom at least as long as the stairs are wide

Don't forget that you will need 100mm rockwool suspended on chicken wire between the floor joists

Oh, ok, actually someone else did say to me today that it had been revised. What about self closers on doors to existing habitable rooms?

+400 if the door opens to the stairs?

Good point re the sound insulation.

Mark: got your email, it crashed my pc when I tried to download the pic will look at it when I'm back in the office in the morning.

 

[^woody^]

All doors on the escape route have to be min FD 20 but no self closers are required.

And the rockwool is not sound insulation (although it helps) its fire insulation - the chicken wire holds it in place if the ceiling goes

 

[mhuk]

I uploaded the image to here if it's easier (and thanks for taking the time to look).

Sound insulation is an important factor for me (maybe more for the roof, but also to prevent any noise annoying the neighbours. Would some extra plasterboard under the rockwool help (both for fire retardation and some extra sound attenuation)?

 

[mhuk]

I'm still waiting to hear from the BCO, but in the meantime I've been thinking about stairs.

My ceiling is 2600mm and assuming a rise of 220mm and going of 220mm, do you think these (plus bannisters etc) would do the job of accessing the loft from my hall (and meeting BR), with step 8 being approx in line with the left hand door in the 2nd photo in my second post:

There would be a plasterboard partition walls with an FD30 door in the loft itsef, as per BR. The doors to the bathroom and bedroom would be moved a new partition wall added for altered access.

Apologies for the poor PhotoShop mock-ups

 

[allloft]

Hi
Remember that you will increase your height when you add your new floor above the ceiling,so you may need another riser and you will have to increase the go if you have a 220mm rise as they will be to steep.
I always advise anyone to go down the building regs route as the room can be classed as habitable therefore increasing your homes value,you also know it is safe to use.If you dont at the very least fit interlinked smoke detectors at all levels they are only about £12.00 each