First floor joists floorboards

[stavros.london]

Hello forumites,

I am renovating my home and have started lifting some of the chipboard floorboards in the first floor. My plan is to insulate with 25mm boards between the joists, and then install underfloor heating on top of the insulation which will require another 25mm. I am also considering removing the ceiling downstairs and instead put new 9mm ceiling boards in between the joists so that I expose the joists partially in the groud floor living area. The joists are 16cm in height so the insulation, UFH, and between-joists ceiling arrangement will leave around 100mm of joists exposed.

My concerns:
- I was thinking of installing 38mm x 38mm battens on the side of the joists in order to screw the ceiling boards form underneath. Would this suffice or do I need something more?

- The existing joists have some herringbone struts in between them but they seem all over the place right now with some missing and others with only the half part in place. I assume these serve some sort of structural support, but could I remove or replace them with straight noggings? Any other suggestions that will allow me to expose the joists "neatly" rather than with noggings and struts visible?



- The joists where they rest on the wall, have this darkened colour (as per photo). What is this? I measured the moisture with a meter and comes up the same across all areas at around 6-8% which I believe is normal.



- Since the joists are exposed like that, should I be looking to do something to "protect" them, mainly from damp, or anything else I could to insulate and make this more airtight? Finally, how are the joists supposed to be ventilated since there are no airbricks?

Many thanks in advance!

 

[geraldthehamster]

- I was thinking of installing 38mm x 38mm battens on the side of the joists in order to screw the ceiling boards form underneath.

Here's another option, to avoid disturbing the ceiling structure (or compromising its fire resistance):

Under-board the joists. Screw rough-sawn 2x2 or 3x2 to the bottom of the joists through the plasterboard. Conceal screws by splitting out a hinged chunk with a chisel, where each screw is to go, drill and screw, then glue hinged chunk back. Get ceiling skimmed between timbers. I haven't done this but I know someone who has.

Cheers
Richard

 

[Deleted member 174758]

Agreed. It is never a good idea to affect the fire integrity of a floor this way. The technique you refer to is called secret nailing and it works but the OP will need to be careful not to use too much glue and to wipe of any squeeze-out immediately if he is not to banjax any chance of staining or clear finishing the joists subsequently without nasty light areas under the finish where glue has dried into the grain. Sanding rarely removes 100% of this residue

The solid strutting (incorrectly referred to as noggins by the OP) needs to be the same cross section as the original joists if at all possible but in any case must be at least 70% of the depth of the original joists to be effective. Solid and herringbone strutting do fulfil a purpose - they make the floor stiffer and less bouncy and so they shouldn't just be removed on a whim (or for that matter by a plumber or a sparky)

 

[stavros.london]

Thanks to both for the replies. I've been convinced and will not try to expose the joists after all.

Any advice on the other questions though: what is that darkened section at the ends of the joists? And do first floor timber joists need ventilation and how is this achieved? Do I have to protect them from damp somehow?

Many thanks!

 

[Deleted member 174758]

Difficult to tell from a photo, but possibly the joists ends have been treated with something line boiled linseed oil or a damp proofer with has made them darken

 

[catlad]

Good luck trying to get people in Lancashire to start calling noggins anything else.

 

[Deleted member 174758]

I served my time in south west Lancashire and solid strutting was called just that (as opposed to herringbone strutting) - if you called them noggins you were just considered a bit thick because noggins are in walls. But then that was 40 years ago.