Replacing joists like for like - building regs?

[leedjc]

Hi all!

We are renovating our house and after lifting the floorboards, have found a couple of the 1st floor joists to be deflecting quite badly due to woodworm etc. My question is, do we need to respec the joists to comply with current building regs?

If so, would this be the case if we only replaced one or two? I'm quite happy to replace all of them, but have an issue if we have to replace the current 5" ones with 8-9". The only way is up in our house, don't really want to raise floors by 3-4" upstairs.

PS house is early 1800s

Thanks!
Lee

[big-all]

you can update by say 300 centers as opposed to 400mm centers or whatever the tables say or you think will help

[Job and Knock]

Very often really old houses have under-sized joists, especially the artisan dwelling sort of property. What sort of span are you talking about and at what centres (currently)? From those someone can at least give you a ball park for the size of joist you should have. A 5in joist is really pretty small by today's standards

[leedjc]

Span is 3500mm and current centres vary around 600-650mm.

I had a chat with building control today and it seems that any less than 50% joist replacement is a repair and they won't need to be involved.

I don't need to replace more than 50% of joists, but ones that don't need replacement are somewhat bowed. It will will a lovely job getting the new floor level! I'm very tempted to replace all joists, but want to avoid bringing the floor level up upstairs too much.

The original floor was 20mm floorboards, then carpet. I am looking to lay 18mm P5 flooring and 18mm engineered wood flooring, so the new height on original joists would be higher already!

The other consideration is that we want exposed beams downstairs, so reducing the centres isn't really an option as we want it to look as original as possible....

[Job and Knock]

600 to 650mm centres and 5in joists on 11ft span? All I can say is put the water bed on hold! On 600mm centres the minimum recommended joist size is something like 195 x 50mm (Source: Haynes and Building Regs table A1), depending on active load - and that's assuming something like C16 (SC3) graded (although C24 (SC4) would be better if you can find it - more rigid). In other words your flooring joists are somewhat inadequate and I'd lay odds on it that the floor feels "bouncy". If you are in investigation mode I'd consider taking a look at the ends of the joists to check for any decay (based on my own experiences on my last house where I had tpo replace all the upstairs joists completely). That may help you decide on your needs

[big-all]

the only two options to keep replacements below 50% is to replace the rotten and halve the centres
or introduce support centre span

as an aside

if possible [and un notched]turn the sag upwards so the new joists and gravity will act together to level the floor rather than fighting gravity to try and pull upwards

[leedjc]

Thanks for the help guys. After much deliberation today, we've decided to just bite the bullet and replace all the joists. Anything less is really a compromise. I've gone for 75x175 joists to keep the centres as far apart as poss to try and keep the look right downstairs.
Once up I'll "distress" the timber to make it look something closer to the original timber.
It's a real shame as I wanted to keep original timber as it's got loads of character, but a lot of it is just too far gone to make it an easy job :/

[big-all]

new joist new ceiling and plant the old timbers underneath at say 800-900 spacings to give the feel you want just split the ceiling into the number off timbers you can use

also dont forget you will have a step upstairs at some point and all your doors will need replacing

[leedjc]

new joist new ceiling and plant the old timbers underneath at say 800-900 spacings to give the feel you want just split the ceiling into the number off timbers you can use

Ah, that's an idea

[wine~o]

The original floor was 20mm floorboards, then carpet. I am looking to lay 18mm P5 flooring and 18mm engineered wood flooring, so the new height on original joists would be higher already!

The other consideration is that we want exposed beams downstairs, so reducing the centres isn't really an option as we want it to look as original as possible....

Regardless of your original question, if you are really going this route (Exposed beams and wooden flooring upstairs)

Then be aware that any noise from upstairs will be an issue..

Off topic I know but worth thinking about.

[Rorschach]

The original floor was 20mm floorboards, then carpet. I am looking to lay 18mm P5 flooring and 18mm engineered wood flooring, so the new height on original joists would be higher already!

The other consideration is that we want exposed beams downstairs, so reducing the centres isn't really an option as we want it to look as original as possible....

Regardless of your original question, if you are really going this route (Exposed beams and wooden flooring upstairs)

Then be aware that any noise from upstairs will be an issue..

Off topic I know but worth thinking about.

Yes, having been in houses with this arrangment I can attest to that.

If you go the new ceiling route though using the old joists as decoration essentially then you should be able to add insulation in the new ceiling to help with noise.

[steviejoiner74]

If you are planning to lay engineered flooring(and nail it) then 18mm chipboard won't cut the mustard.
You'll need minimum 18mm plywood as its not adviseable nailing engineered flooring to chipboard.