Board Loft or Loft Conversion

[Justin Hughes]

Can anyone advise me on the difference in cost between simply boarding a loft and "doing it right" and putting a proper floor down?

I have a 1905 terrace with a loft area of around 13 ft square. Loads of head height up there! The joist situation looks a bit on the light side though, with only two joists actually spanning between the two boundary walls (and which don't seem to be sitting above supporting walls). Between these two hefty joists (at least 6" thick) are attached smaller ceiling joists (about 4" thick) at 2 ft intervals.

Given the above, even if I just want to shove a couple of dozen boxes up there I am a little worried that there is not a lot of strength. Who knows what the future might be, and we may want to properly convert this space in a few years, so I was thinking of putting in a proper floor now. Can anyone hint at what this might involve / cost to do DIY-style? I can see the only real extra cost being in the new joists. Do I need an engineer/architect to design it?

Am I in danger of doing it now and the regs changing in a few years, rendering my work obsolete? Will I need to get a building control officer in now?

Thanks,

Justin

[pjdesign]

I

Justin. This may be of help.

[John Rumm]

What the OP describes is different in two substantial ways: it does not sound like he has a loft made with modern roof trusses, and, he is asking here first.

To the OP:

Chances are you could board over what you have for light storage purposes, but you would want to be careful with how much load you add. Knowing the lengths of the existing beams would help.

A loft area of 15 sq foot sounds very small (i.e. a house five feet deep by five feet across) are you sure that is right?

Putting is a proper floor is in itself not that difficult. However access to get the timbers in may be - typically with a loft conversion you have scaffolding and can get access through the outside of the roof.

If you were contemplating a conversion later then it might be worth doing the floor right now so that you have less to do later. If you are not at this stage creating a habitable room, and there is no fixed access to it, you would probably not come under building control. However it might be worth checking with them first. If this was going to be a precursor to a conversion later, then it might be worth getting a BCO involved anyway to save the possibility of doing rework later.

To do a conversion you will need to submit plans (with detailed calculations to prove adequacy) that show the floor design. Again you could get those (or at least the floor design) done now.

[nog]

Didn't he say 13 ft square? That's 169 sq ft.

[John Rumm]

As in 13x13... could be, makes more sense that way ;-)

(I read the "13 ft square" as 13 sq feet which sounds more like a cupboard than a house)

[nog]

When I was a lad, they made a great fuss in school, during breaks from beating the shit out of us, about the difference between n-feet square and n-square feet. Now, of course, the SI convention is n M^2, meaning n-square feet (or is it t'other way around), so it's no longer so clear. :-(

[nog]

Yeah, that's n square metres, of course. :-)

[Justin Hughes]

It's 13ft x 13ft. Sorry they obviously didn't beat it into me hard enough at school.

Being almost a perfect square, and with no trusses (those are the diagonal uprights yes?), it makes a huge space. Back to the floor... The two joists which span the party walls are approx 13 foot long. The ceiling joists between them are probably 11 foot long.

Can anyone suggest costs for the design of a floor and do the BCO charge a fee?

[John Rumm]

Trusses are pre-formed roof memebers - they comprise the floor, rafters, and lots of corss bracing all in ono "unit". Many modern builders seem to like them because you simply crane a bunch of them onto the top of your house and you have a complete roof structure with very little bespoke joinery required. For loft conversions they are a pain because of all the cross bracing and also the very skimpy timber they are normally made from.

Given the age of your property it is pretty unlikely that you have them! You may still get some cross braces in older houses - but these are much simpler to deal with.

Do these joists pass over the other loft joists? or do the ceiling joists actually stop at these beams?

If your ultimate loft conversion is not going to involve a dormer and is just a case of adding a new floor, lining the roof, creating access, and adding a few roof windows, then the floor design should be quite simple (in comparison to how it could be!).

With some research and the right software, you may be able to do the design yourself, or failing that find an architect (or a lower cost varient of) to do the design. Costs vary - a full blown architect could cost 500 or so. BCOs charge a fee for a full plans submission. Flat rate round here is 264. That includes as many visits as required from the BCO.