What type of timber to use on floor joists?

[Tom_2018]

i need to raise the level of a floor by an inch. The room is currently empty ready for decorating and has bare floorboards.

I intend to take up the boards and fix a piece of timber to the top of each joist before fixing the boards back down.

Is untreated rough sawn timber suitable for this purpose or do I need something stronger eg hardwood or treated timber?

 

[motorbiking]

It depends on the spacing and the floorboards. Depening on the room size and age of the floorboards, it might be easier to simply overboard. Is this ground floor or 1st floor and is the void insulated or above a warm room?

If its cold/ventilated, I'd be using treated timber.

 

[Tom_2018]

Thanks biking,

It’s a ground floor room. The joists and boards are in good condition. It’s an old house, Georgian, I don’t know if the boards are originals but they’re certainly nice and chunky and so i’d quite like to keep them on top, maybe sanded or painted.

There is a cavity under the boards maybe a foot deep, then what looks like rubble (but I haven’t lifted the entire floor yet).

So in terms of treated timber is there any particular type or just anything that’s rot-proof? Would roifing battening work?

 

[tony1851]

If it's 18th century, is it listed?
If so, you would need approval for this.

 

[motorbiking]

if you are lifting the boards to a vented void then definitely go for treated battens and take the option to insulate between the joists while you can, particularly if you are just having sanded floor boards.

 

[motorbiking]

example here: http://www.yougen.co.uk/blog-entry/2301/Insulating+under+the+floor+-+a+photo+case+study/

 

[Notch7]

Just use 50 x 25mm battens, sawn, treated

They are generally pretty accurate to the size.

 

[Tom_2018]

Many thanks all, really helpful

 

[motorbiking]

and lag any pipework you find.

 

[Tom_2018]

having spent yesterday taking up all the floorboards, there are actually a couple of partially rotten joists down there. I could either repair sections or replace entirely. The existing joists are 48x100 approx.

This is probably a really stupid question, but is there such a thing as a "joist" timber? Or is joist just the term given to regular timber used to hold up flooring?

I guess what i'm asking is, to replace the rotten joists is a length of treated C16 timber sufficient. Like this one.

 

[motorbiking]

what is the spacing? It really depends how far apart they are and the gaps between any pillars. You can only replace with a similar size, if you are worried about spacing you can install them in pairs. C16 is fine, I wouldn't want them spaced any more than 400-500mm tops.

e.g.

I would personally cut out the rot and then add a sister joist along side.