To ventilate or to waterproof?

[RachelMerrywinkle]

I understand the case for ventilating old properties over waterproofing them as a means of keeping the damp down. However - we have no chimneys so one of the main sources of constant ventilation is missing.

We were going to pull up the concrete floor in the basement of the house we are buying and see if we can get it back to floorboards (if there are floorboards), but now we are having second thoughts.

With no chimneys, would everyone still avoid damp proof membranes or is there a case for them?

 

[montyjohn]

If you've got concrete over floorboards, you'll probably find everything below is rotten. Maybe if it's a recent addition you'll be in luck, but I'm not so sure this practice would happen these days.

If it was me, I would pull the concrete up and just assume that it will need new boards and joists below. But knowing the boards are probably junk, it would be low on my list.

Just thinking aloud, but maybe an alternative would be to core drill a couple of large holes (at opposite ends) and pump air through below. You could then just ignore it for as long as you like.

 

[RachelMerrywinkle]

If you've got concrete over floorboards, you'll probably find everything below is rotten. Maybe if it's a recent addition you'll be in luck, but I'm not so sure this practice would happen these days.

If it was me, I would pull the concrete up and just assume that it will need new boards and joists below. But knowing the boards are probably junk, it would be low on my list.

Just thinking aloud, but maybe an alternative would be to core drill a couple of large holes (at opposite ends) and pump air through below. You could then just ignore it for as long as you like.

Thank you. It’s a habitable basement so could we lay a floor over the concrete?

 

[montyjohn]

Thank you. It’s a habitable basement so could we lay a floor over the concrete?

You could, but you will still have a damp void underneath with decaying timbers and moisture being driven into your walls through the foundations.
If you vent below the floor I see no problem adding any floor you like on top of the concrete.

Whilst concrete is often described as a vapour barrier, it still does let vapour through, albeit slowly. So I would only put a breathable floor on top of the concrete otherwise you are creating another mould trap.

Or are you talking about a suspended floor on top of the concrete? If going to this expense, may as well just do it properly and remove the old concrete.

 

[Cubist]

Dumb questions perhaps but -
Why do you believe there is am old wooden floor buried under concrete in that basement?
Also, is this the same basement included in your first post to this forum?

 

[RachelMerrywinkle]

Dumb questions perhaps but -
Why do you believe there is am old wooden floor buried under concrete in that basement?
Also, is this the same basement included in your first post to this forum?

Not a dumb question - and yes it’s the same property. I’m assuming floorboards based on the age (1860s) and air vents and (removed) fireplaces in the basement. Totally open to other suggestions as I’m a complete novice….

 

[Cubist]

Air-bricks were first introduced for use in the UK in the late 19th Century which neatly corresponds with when this house was built. The presence of any such in the external walls would also seem to confirm that some, perhaps all, of the floors were of a suspended wooden type. However, I'm puzzled as to why you would have concluded or been told that this wooden floor has simply been buried in concrete? Also, I previously noted that this basement contains a number of modern kitchen cabinets - is there any evidence of swelling and/or blackening of the cabinet edges in contact with the floor?

 

[RachelMerrywinkle]

Air-bricks were first introduced for use in the UK in the late 19th Century which neatly corresponds with when this house was built. The presence of any such in the external walls would also seem to confirm that some, perhaps all, of the floors were of a suspended wooden type. However, I'm puzzled as to why you would have concluded or been told that this wooden floor has simply been buried in concrete? Also, I previously noted that this basement contains a number of modern kitchen cabinets - is there any evidence of swelling and/or blackening of the cabinet edges in contact with the floor?

I think i assumed the floor had been covered because that’s what had happened in our current house. Is it more likely that the floorboards would have been removed before concrete was added do you think? I’m not sure about the state of the cabinets - we’ve not been in the property for a few months but we will be going in soon and I’ll have a look.

 

[Cubist]

Best practice would be to remove all the timber, floorboards and joists, before pouring concrete but - as you already know - some people donate apply best practice rules. When you're next there 'tap' the floors with wooden stick while listening for any hollow sounds. Also, check those cabinets for swelling and/or blackened sections - this would indicate damp that MAY be rising from the concrete floor. If they are in good condition and were not installed last week then you probably do not need to excavate the floors. You may then also install a 'floating' wooden floor without too much trouble.

 

[montyjohn]

The way to tell is to jump up and down on the floor.
You can feel boards under concrete.
Concrete direct on the ground as a solid and dull sound when you jump on it.

 

[Cubist]

I do not wish to appear alarmist @RachelMerrywinkle but; Please, DO NOT jump up and down on that, or any other floor, before you know definitively it can stand that kind of demand. Many people have suffered severe injury and, in some rare circumstances, been killed doing this.

Right now you do not know whether that floor is a solid and heavy slab of concrete or a thin screed laid over the top of a rotten wood cavity of indeterminate depth - there could even be another cellar down there.

 

[Stevers]

Our basement (originally a sort of downstairs kitchen wing) had a concrete screed over stone flags. It's much more likely that a habitable basement would originally have had a practical brick, tile or stone floor as it would be difficult if not impossible to provide sufficient ventilation to a timber suspended floor even in a semi-basement. Has anybody reading this ever come across a timber suspended floor in a basement, or actually concrete laid on a timber suspended floor?

 

[Kearn]

Basements, in the true sense underground, were never habitable dpaces and still cannot be. They are are by their very nature damp, cool spaces, great for wine and certain storage, not for humans and moisture. They need great, cross flow ventilation

Equally, being cut into the ground, they would never have had suspended timber floors, just brick / tile / stone flags directly laid on the soil.

The walls would also be intended to evaporate moisture from the built up ground behind, so need to be able to moisture manage - lime plaster/limewash only.

Chimneys are not the only source of ventilation in an old building. Why do you have none, out of interest?

Tanking, injections, creams and all the modern snake oil approaches to ‘combatting damp’ do not work. They don’t deal with or understand the causes, just try to temporarily hide the symptoms. They waste money and do damage.

 

[RachelMerrywinkle]

Best practice would be to remove all the timber, floorboards and joists, before pouring concrete but - as you already know - some people donate apply best practice rules. When you're next there 'tap' the floors with wooden stick while listening for any hollow sounds. Also, check those cabinets for swelling and/or blackened sections - this would indicate damp that MAY be rising from the concrete floor. If they are in good condition and were not installed last week then you probably do not need to excavate the floors. You may then also install a 'floating' wooden floor without too much trouble.

Our basement (originally a sort of downstairs kitchen wing) had a concrete screed over stone flags. It's much more likely that a habitable basement would originally have had a practical brick, tile or stone floor as it would be difficult if not impossible to provide sufficient ventilation to a timber suspended floor even in a semi-basement. Has anybody reading this ever come across a timber suspended floor in a basement, or actually concrete laid on a timber suspended floor?

The Victorian house we are in now has floorboards in the basement. They have been boarded over and screeded in the kitchen, but in the other rooms we took the carpets up and there were the floorboards. It’s probably my wishful thinking that this new place would be the same.

 

[Stevers]

Basements, in the true sense underground, were never habitable doves

True of 'cellars' perhaps rather than 'basements'.

 

[RachelMerrywinkle]

Basements, in the true sense underground, were never habitable doves and still cannot be. They are are by their very nature damp, cool spaces, great for wine and certain storage, not for humans and moisture. They need great, cross flow ventilation

Equally, being cut into the ground, they would never have had suspended timber floors, just brick / tile / stone flags directly laid on the soil.

The walls would also be intended to evaporate moisture from the built up ground behind, so need to be able to monster manage - lime plaster/limewash only.

Chimneys are not the only source of ventilation in an old building. Why do you have none, out of interest?

Tanking, injections, creams and all the modern snake oil approaches to ‘combatting damp’ do not work. They don’t deal with or understand the causes, just try to temporarily hide the symptoms. They waste money and do damage.

Basements, in the true sense underground, were never habitable doves and still cannot be. They are are by their very nature damp, cool spaces, great for wine and certain storage, not for humans and moisture. They need great, cross flow ventilation

Equally, being cut into the ground, they would never have had suspended timber floors, just brick / tile / stone flags directly laid on the soil.

The walls would also be intended to evaporate moisture from the built up ground behind, so need to be able to monster manage - lime plaster/limewash only.

Chimneys are not the only source of ventilation in an old building. Why do you have none, out of interest?

Tanking, injections, creams and all the modern snake oil approaches to ‘combatting damp’ do not work. They don’t deal with or understand the causes, just try to temporarily hide the symptoms. They waste money and do damage.

There might be a different word for what we are dealing with other than “basement”. Almost all the Victorian houses in our area have a “basement” that people live in. Half of them have been converted into flats. The walls are not touching ground, they’ve been completely dug away. I heard that this is how they were originally built - to house the kitchen instead of an extension at the back of the ground floor. They also contain fireplaces. We currently live in a “basement” maisonette, which indeed has floorboards covering the whole thing - I’m guessing it’s suspended as the guy who sanded it advised us not to fill the gaps between the boards.

The house we are trying to buy has unfortunately been the victim of 70s “renovation” - half the chimney breasts removed as well as the chimney stack. It shouldn’t be allowed in my opinion!

 

[Stevers]

We currently live in a “basement” maisonette, which indeed has floorboards covering the whole thing - I’m guessing it’s suspended as the guy who sanded it advised us not to fill the gaps between the boards.

And you haven't had to take a single board up to do anything to the services, so you could take a look at what's underneath? With air all around them these must be basements in the sense that the 'ground' floor is really the first floor, but has the reception rooms and very often steps up to the front door.

 

[Kearn]

True of 'cellars' perhaps rather than 'basements'.

Yeah true, but without pics hard to tell what the words mean and many see them as interchangeable.
Still, we’re talking bottom of the building, likely under ground levels to some extent, struggling with airflow certainly at the floor level…