I know I need a 10mm expansion gap around a chipboard floor, skirting hides that so no problem. However, it joins a concrete floor in the middle of the room. How do I accommodate this? No gap, or is there another solution?
Chipboard floor butted against concrete floor - expansion gap?
- Thread starter ben1979
- Start date
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Yes you will need a 10mm or so expansion gap.
What is the concrete doing there?
Do you intend to cover the concrete surface with some kind of finish flooring or just run underlayment and laminate across?
Depending on the answers to the above then there's various ways of dealing with the gap.
What is the concrete doing there?
Do you intend to cover the concrete surface with some kind of finish flooring or just run underlayment and laminate across?
Depending on the answers to the above then there's various ways of dealing with the gap.
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The concerete is the floor for one half of the room. Actually it's the screed shown and looks to be the gypsum based suff. The original room was extended at some point with the new having a concrete/gypsum floor whilst the original had suspended timber. The old floor rotted (issue causing this since resolved) hence the need for replacement. The whole lot will be covered with an underlay & then laminate.
OK, well that post #5 info might change things.
Here's an option for what to do next if you want:
1. take a pic of the whole room as it is.
2. lift a sheet of the unfixed chipboard & take a pic through the suspended floor joisting into the sub-area.
3. take a pic outside at ground level showing any air bricks.
I say the above because a number of OP's with similar situations dont always take the best precautions with previous issues and a split floor - i can also see a possible glaring issue in your pic.
Anyhow, whatever you want is fine.
Here's an option for what to do next if you want:
1. take a pic of the whole room as it is.
2. lift a sheet of the unfixed chipboard & take a pic through the suspended floor joisting into the sub-area.
3. take a pic outside at ground level showing any air bricks.
I say the above because a number of OP's with similar situations dont always take the best precautions with previous issues and a split floor - i can also see a possible glaring issue in your pic.
Anyhow, whatever you want is fine.
Last edited:
Thanks. Struggling with some of those images, but have a couple.
Sub area - isn’t great. There is a concrete oversite, not as dry as it could be, looks doubtful there is any dpc under that, but seems ok. External walls and piers are dry to well below joist level.
Airbricks have been blocked up by the concrete floor. Not ideal I know. There are some at the front of 5he property and these are clear, but nothing at the back and no way to reinstate these.
Hopefully you are going t9 tell me the glaring issue is the board in the first picture needs cutting. That’s been done.
Sub area - isn’t great. There is a concrete oversite, not as dry as it could be, looks doubtful there is any dpc under that, but seems ok. External walls and piers are dry to well below joist level.
Airbricks have been blocked up by the concrete floor. Not ideal I know. There are some at the front of 5he property and these are clear, but nothing at the back and no way to reinstate these.
Hopefully you are going t9 tell me the glaring issue is the board in the first picture needs cutting. That’s been done.
Attachments
Sorry, to be bearing bad news.
Without a plan view of the kitchen that shows, hopefully, two outside walls its difficult suggesting how to ventilate the sub-area. And the main house sub-area beyond.
Perhaps there's a short stretch of outside wall next to the suspended floor - if there is then a couple of air bricks could be installed, and the joists drilled for a little through ventilation. A bit like flat roof joists are sometimes vented.
The joists seem to be sitting on the oversite with no isolating DPC strips below each joist.
The joists should have been strung across the room to pick up any possible outside wall air brick ventilation.
The insulation in the joist bays will have to be removed - why? Because I've repaired countless ground floors
rotting away due to insulation choking off any air flow.
From what i can see, the oversite below the joists appears to be sand and lime or cement - has gypsum plaster also been mixed in? The surface of the oversite can be seen shelling off?
You mention damp conditions and the possible lack of a membrane (a DPM) - this damp will have to be sourced & dealt with. It could be condensation?
When the concrete floor half was poured then 100mm ventilation tubes should have been inserted to carry fresh air to the sub-area.
Without a plan view of the kitchen that shows, hopefully, two outside walls its difficult suggesting how to ventilate the sub-area. And the main house sub-area beyond.
Perhaps there's a short stretch of outside wall next to the suspended floor - if there is then a couple of air bricks could be installed, and the joists drilled for a little through ventilation. A bit like flat roof joists are sometimes vented.
The joists seem to be sitting on the oversite with no isolating DPC strips below each joist.
The joists should have been strung across the room to pick up any possible outside wall air brick ventilation.
The insulation in the joist bays will have to be removed - why? Because I've repaired countless ground floors
rotting away due to insulation choking off any air flow.
From what i can see, the oversite below the joists appears to be sand and lime or cement - has gypsum plaster also been mixed in? The surface of the oversite can be seen shelling off?
You mention damp conditions and the possible lack of a membrane (a DPM) - this damp will have to be sourced & dealt with. It could be condensation?
When the concrete floor half was poured then 100mm ventilation tubes should have been inserted to carry fresh air to the sub-area.
Thanks Tel, really grateful for your advice on this.
I’ve attached a plan which hopefully sets out where everything is. Unfortunately no external walls against any of the timber floor so it’s really not easy. I’ve marked the easiest point to add through ventilation on my sketch, not ideal, but I think it would work if I really need it. Still involves breaking up a fair bit of concrete floor, but significantly less than putting vents to the rear of the property as that’s a 4m stretch. Yes, I thought ventilation tubes should have been put in when it was being built. I questioned this with the builder at the time who told me these weren’t necessary as there was plenty of ventilation at the front. Didn’t really buy this theory at the time, guess I should have insisted on them!
The joists aren’t sitting on the oversite. There are 3 honeycomb piers under them keeping them approx. 40cm above it. The top of each pier is blue brick and I’ve put plastic DPC on top of this before laying the joists. These were dry anyway, the cause of the original rot appeared to be via the (previously) external wall where plaster debris, etc. was bridging the joist ends with the wall below the blue bricks. Along with a leak due to rainwater which is now resolved.
Yes, I think oversite below the joists is sand and cement, looks like a weak mix, but seems ok. – Yes, you can see gypsum shelling off. The floor screed from the new floor had been allowed to overflow under there and was mixed in with various rubble that the builder had dumped under there. I’ve removed all of this and chipped back the screed as far as possible.
The only remaining cause of dampness I can see possible is from the soil under the oversite. Given it seems of poor quality and the presence of any kind of membrane having been laid is unlikely (1950’s?) Yes, it could be condensation though, hadn’t thought of that. This doesn’t appear to be getting near to the timbers though. When removed, the old joists were raised on the piers using scraps of floorboard, so untreated. These were not showing signs of decay.
I’ve attached a plan which hopefully sets out where everything is. Unfortunately no external walls against any of the timber floor so it’s really not easy. I’ve marked the easiest point to add through ventilation on my sketch, not ideal, but I think it would work if I really need it. Still involves breaking up a fair bit of concrete floor, but significantly less than putting vents to the rear of the property as that’s a 4m stretch. Yes, I thought ventilation tubes should have been put in when it was being built. I questioned this with the builder at the time who told me these weren’t necessary as there was plenty of ventilation at the front. Didn’t really buy this theory at the time, guess I should have insisted on them!
The joists aren’t sitting on the oversite. There are 3 honeycomb piers under them keeping them approx. 40cm above it. The top of each pier is blue brick and I’ve put plastic DPC on top of this before laying the joists. These were dry anyway, the cause of the original rot appeared to be via the (previously) external wall where plaster debris, etc. was bridging the joist ends with the wall below the blue bricks. Along with a leak due to rainwater which is now resolved.
Yes, I think oversite below the joists is sand and cement, looks like a weak mix, but seems ok. – Yes, you can see gypsum shelling off. The floor screed from the new floor had been allowed to overflow under there and was mixed in with various rubble that the builder had dumped under there. I’ve removed all of this and chipped back the screed as far as possible.
The only remaining cause of dampness I can see possible is from the soil under the oversite. Given it seems of poor quality and the presence of any kind of membrane having been laid is unlikely (1950’s?) Yes, it could be condensation though, hadn’t thought of that. This doesn’t appear to be getting near to the timbers though. When removed, the old joists were raised on the piers using scraps of floorboard, so untreated. These were not showing signs of decay.
Attachments
Thanks for the plan view.
Condensation sometimes takes its time but it can rot out timber given enough time.
If the RH side front elevation vents are venting all the way to the kitchen floor then you could cut into the floor a couple of kitchen floor vents to create some through ventilation.
Protecting the original kitchen floor:
The old RH side wall may have had air bricks to vent that side of the house?
Is the LH side of the house open or a party wall? If its open then install air bricks.
The answer to the original question is: allow the 10mm all around at all abutments and about 6mm at the solid floor.
Then do you laminate etc as you intended.
Given equal levels across the solid and suspended halves then just allow the flooring to roll over the gap.
Condensation sometimes takes its time but it can rot out timber given enough time.
If the RH side front elevation vents are venting all the way to the kitchen floor then you could cut into the floor a couple of kitchen floor vents to create some through ventilation.
Protecting the original kitchen floor:
The old RH side wall may have had air bricks to vent that side of the house?
Is the LH side of the house open or a party wall? If its open then install air bricks.
The answer to the original question is: allow the 10mm all around at all abutments and about 6mm at the solid floor.
Then do you laminate etc as you intended.
Given equal levels across the solid and suspended halves then just allow the flooring to roll over the gap.
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