Damp proof (membrane) for floorboards

[Aaron King]

Hi smart guys,

I am totally innocent for interior design and DIY. I want to change the carpet to solid wood flooring for my bedroom.

Currently, there are floorboards below the carpet, and I think I should lay the solid wood flooring above the floorboards after I remove the carpet.

Unfortunately, I found there are damps on the floorboards. Some of the floorboards also need to be replaced. I searched online and found something called 'damp proof membrane'. However, lots of discussions saying that this kind of 'damp proof membrane' is suitable for damp proofing concrete floors above ground, but NOT for the floorboards.

I also checked the situation below the floorboards, there are quite a lot of empty space there and I don't think I should remove the floorboards and put on the concrete.

So my question is: what is the best option for me now? I want to keep the underlying floorboards (replacing some broken ones). Before I put on the solid wood flooring, which kind of damp proof (membrane) I should apply? Please give me a link to the product if possible. Any other suggestions please let me know. Thanks very much for your help.


A.

 

[blup]

You won't be using concrete on a bedroom floor (unless it's ground floor) as the weight would be too great for the joists to support.

You need to identify the cause of the damp by lifting the floorboards and looking for the source. If it is at first floor level you might have a leak from a water or drainage pipe. Then decide on what needs replacing/repairing. It may require a professional in if you're not able to tackle this kind of work, but at least you may be forearmed with knowledge of the cause of the problem, and that will help in assessing the different causes and solutions that different professionals are likely to put forward.

A DPM would retain the moisture and make things worse.

Blup

 

[Mr Chibs]

If laying on a ground floor straight onto the joists, you need to sort the damp out first, have you got air vents to the outside walls, are they clear?

Once you've got the damp sorted, you could put insulation (rockwool) between the joists, then a building paper (like two sheets of brown paper with bitchumen in the middle) could be used to cover insulation, then floorboards back on, or hardwood floor nailed directly to joists, if thick enough.

Have you got any pictures?

 

[Aaron King]

Thanks for both of you. Your suggestions are very helpful.

Just want to confirm with you that the bedroom is on the ground floor and currently the floorboards are sitting on the joists directly (I will double check if any insulation or anti-damp been done before). I wouldn't try to put on concrete on the floorboards as already suggested that it will be too heavy for the joists to support.

I will take Mr Chibs's advice:

1. I will check if air vents to the outside walls are clear and sort out the damp first.

2. When you say rockwool insulation between the joists, will there be any healthcare or safety issue for using the rockwool? (I mean is rockwool poisonous and flammable?) If possible, please suggest an alternative even if it will be more expensive.

3. When you say building paper (like two sheets of brown paper with bitumen in the middle), do you have a recommendation which one I should use?

Again, sorry to ask stupid questions. I will try to take some pictures after work today. Thanks so much for your help!


A.

 

[Mr Chibs]

Rockwool will be fine, I've been using knauf loft insulation, around 150mm deep (as joists), staple chicken wire under joists to make hammock like troughs, plonk in insulation, tight to joists, cover with builders paper and then do your flooring.

I'm laying a solid oak floor, direct to joists.

There is no poisonous issues or fire!
Do not use polystyrene, as that it's highly flammable.

You can use celotex, but it's around 6 times to price.


https://www.wickes.co.uk/Ndc-Bitumen-Backed-Building-Paper-10m-x-1m/p/141075

https://www.wickes.co.uk/Knauf-170mm-Standard-Top-Up-Loft-Roll-Insulation---6-47m2/p/109450

Ask away if you need more info.

 

[JohnD]

Damp on a floor might be caused by a leak such as a radiator pipe, or round a bay window, sometimes a puppy. Water generally runs downhill so unlikely to be travelling up from under the floor unless it is grossly wet down there.

 

[Aaron King]

@Mr Chibs, thanks for the keywords you provided and I checked online and found something really interesting and similar to my situation (almost identical to my floorboard:

)

Sorry I can't take any photo today as I got home really late and don't want to disturb my little one. I will check up during the weekend and update my progress. Thanks very much for the help.


A.

 

[Aaron King]

Thanks for your reply @JohnD. I will definitely check again to see where is the source of damp.

 

[Mr Chibs]

I've just done all my ground floors in rockwool, I considered celotex but it was £600 vs £100, rockwool is roughly half the efficiency of celotex, so 50mm celo = 100mm rockwool.

In the end I used barrier mesh to make the hammocks.

Too early to tell what effect its' had on the bills, but just walking on the floor, it feels and sounds different. I've internally insulated all the walls too, so it's toasty now.

Good luck.