Loft conversion, fixing oak boards on to joists? HELP!

[powerbooksub]

Evening all

Advice needed please for loft conversion. It's a mid terrace and the wall/head height is restricted by the roof we share with our neighbours. Unfortunately we are looking at 1.8m which is not great We are therefore looking at every opportunity to maximise this dimension as long as it is safe and complies with building regs.

So, rather than put chipboard down first and oak on top, can we

Q1. Forget the chipboard and fix 20mm oak boards directly on to joists (which are 30-35cm apart)? Can the board be engineered or plank only?

Q2. Convention says the oak boards should be fixed perpendicular to the joists, however is the following possible to allow the oak boards to be fixed parallel to the joists? For example by:

a) Fitting 22mm flooring between joists which is screwed on to 1" or 2" battens which themselves are screwed into the joists creating a "flush" level floor.

or

b) Fixing extra pieces of 6" joist in between the longer joists (using 90deg metal brackets), creating a type of grid pattern, on to which the oak planks can be fixed.

Are these construction techniques permitted?

Thanks

 

[freddiemercurystwin]

What stage is the conversion at? Is that 1.8m existing between top of ceiling joists and underside of roof or top of new joists and underside of new insulation/plasterboard of roof or what? You can't seriously be doing a lofty with only 1.8m headroom surely?

Regarding the flooring normally a T&G board would be specified to provide the fire resistance so your method may work if you can get it past BC and your SE with maybe some further fire proofing but sounds bonkers to me if you'll only end up with 1.8 anyway.

 

[powerbooksub]

Thanks for the reply, I was hoping someone would get in touch. I think I got my numbers wrong, I am looking at 2.2m head height but I would still like to maximise it if possible.

Plasterboard going up this morning and plastering out will be finished today. 26mm T&G quietboard (chipboard + foam) is down but I am happy to remove/discard if I thought I would save 26mm by laying oak boards directly on to joists.

By the way, I have mulled it over and think it safer if I run oak boards at 90deg to the joists. So the only question remains, am I allowed to do this (I know zilch about building regs) and can i use engineered boards or solid planks only?

 

[freddiemercurystwin]

As mentioned you need T&G for smoke/fire reisitance so if your boards are T&G then should be OK. If not then you'll probably need additional measures to maintain the fire reistsnace. Speak to your BCO and see what they'll require to maintain integrity.

 

[Chri5]

Might be totally wrong, but I thought 22mm was required for direct to joist fit?

Also look towards suppliers that offer long boards not those supplies that mix up packs with random lengths between 400mm and 1800mm.

 

[powerbooksub]

Thanks for the advice guys. I will seek out 22mm and long boards.

 

[Chri5]

Have a look at tongue tight screws, they are an alternative fixing to nailing. Used them for about 40m sq of hardwood floor two years back and everything is ultra solid.

Since joists could be 450mm centres or greater the fixing need to be good. Some nail systems suggest 300mm and you aren't likely to get that direct to joists.

 

[JFJFlooring]

Hi Powerbooksub,

Sorry to have joined this convo late but in response to your very first message:

'Q2' 'example b' when you say about using extra pieces of 6" joists between floor joists....... these are known as 'joist hangers' and this method can be used as long as the joists hangers are no more than 400 centres apart.

However, I strongly agree with you that if possible it would be best to have the flooring running perpendicular to the joists.

Also I would advise you to use a high quality engineered oak floor that is structural and can be laid directly onto joists. Structural engineered boards are usually around 21/22mm as you said. Much thinner than your 26mm+.

I would say go for engineered board. If you get the right engineered floor it can visually look just as beautiful as a traditional solid oak floor (if not better) be much much more stable and generally come in longer and wider lengths. There is an article I have wrote on the benefits of engineered wood flooring that you can read if you so wish: http://www.jfjflooring.co.uk/index.php/whatcustsay/79-faqs/77-advantagesofeng

Hope this helps. Thanks, Tom.