Floor insulation in suspended timber floor above Bathroom

Joined
30 Jul 2013
Messages
20
Reaction score
0
Location
Hertfordshire
Country
United Kingdom
Hi there,

I have a 3 bed demi detached house which has the bathroom downstairs under one of the bedrooms above.

In the bedroom above i have 1/3 of the floor boards up as i had some new lights fitted along with an inline extractor fan. The joists are 15CM deep with the ceiling below (bathroom ceiling) being plasterboard. Above are floorboard (not T&G but those with gaps). i then have underlay and carpet on top of the floor boards.

As the carpet is up i am looking to lay some insulation between the joists to keep the heat in the bathroom below.

I have done some research and i can either lay supporting netting between the joists and then lay 10mm loft insulation on this or use Celotex and have it tightly fitted so it is flush with the top of the joists.

My main worry is ventilation and preventing the wood to rot.

if anyone can advise the best way for me to do this without damaging the floor over the years that would be appreciated.

thanks,

Mike
 
Sponsored Links
IMO it is difficult and dusty to cut rigid insulating slab to fit tightly between joists. I would go for loft mineral quilt. I only uset the stuff treated with Ecose which prevents it shedding irritant dust and fibres. It is made by Knauf but some own-brands are the same stuff, I think Wickes are. It is brown, not yellow.

you can lay insulation over electric cables, or under them, but cables must not be surrounded in insulation.

The netting support is used for ground-floor insulation where there is nothing below. Yours can lie on the plasterboard ceiling.i

Bear in mind that if the upstairs rooms are inhabited, then any heat which leaks through the floor will reduce the amount of heat you need to supply, so there are different opinions on whether it is worth insulating between floors. The insulation will make a slight muffling in airbourne noise like conversations and TV.

Seal any holes in and around the ceiling which could allow steam to rise up any it will not get damp. holes are usually around pipes, and those horrible lamps that poke through holes.
 
Thanks for this.

my aim is to not necessarily make it air tight but to keep the heat in the bathroom longer so not worried if it makes it through gaps in the floor.

my main worry from what i have read is ventilation as i dont want the wood to rot.

plz can you advise regarding this and what is the best way to prevent this?

I done a lot of reading on other posts and forums and it would appear a vapor barrier is required?
 
painted plasterboard, with no holes, is fairly resistant to moisture vapour. The more modern foil-backed plasterboard is very resistant.

Moisture barriers are very important when you have a warm moist room with a cold wall, because the cold wall or roof will suffer condensation. But the floor and void will be just as warm as the bathroom, so I don't see a problem here.

You mention that you have an extractor fan. This will pull air into the bathroom from the rest of the house (provided the door and window are shut, as they should be) to replace the moist air it expels.
 
Sponsored Links
Thanks John for your informative advice. Much appreciated!

I am glad you advised to use Knauf Loft roll as this was the one I was planning to use vs Celotex which is relatively inexpensive in comparison to Celotex. In the room above the bathroom i will only need 1 of these http://www.diy.com/nav/build/insula...oll-Loft-Insulation-100mm-Thickness-12057529.

I will ensure that all gaps in ceiling and around lights are sealed. I will be re-decorating the Bathroom sometime next year anyhow so i will also ensure a good waterproof paint is used on the ceiling then also. however as a precaution ill just give it a quick coat after i have done the insulation.

You are correct regarding the extraction Fan, i have a Manrose inline fan rated 240 m3 per hr (i have set a 30 minute overrun also).

I think when i was doing my research i was getting confused with those laying underfloor insulation to the ground floor and thus requiring netting and a vapor barrier
 
Use what's easiest to work with, your joists might not be perfectly straight so roll or slab are probably a better option. My joists are very wonky, I used cavity slabs as easy to cut to width with a Stanley knife, didn't irriate like normal roll fibre and I could get a very good fit. The slabs did specifically for under floor sold in B&Q disintegrate and were impossible to work with.... all depends on how regular your joists are.
 
some of the mineral wool slabs are made by Knauf (though they may be own-branded, e.g. Wickes) with Ecose, which prevents them shedding irritant dust and fibres. I would now use nothing else. Look for the name Ecose on the wrapper.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Back
Top