Keithj
Member
- Messages
- 817
- Location
- Witnesham, Suffolk
I'm posting this for a friend of mine - he's in the process of registering for the forum...
- Thread starter Keithj
- Start date
MatthewC
Member
- Messages
- 1,733
- Location
- Central/South England
That's exactly how my 150 year old suspended floor is constructed, except that the supporting walls for the floor are brick not block. The supporting walls are about three feet apart.
My floor had only one vent, through the 18" limestone wall, and so I added one through the floor on the far side of the room. I don't know if two vents in the floor (on opposite sides of the room obviously) would work, but would be better than nothing!
88v8
Member
- Messages
- 3,131
- Location
- Glorious Gloucs
Yes, blocks, bricks. Include a dpc below the joists, felt will do. Don't let the joist ends touch the wall. Put beams on top of the sleepers, sideways, on a bed of mortar to facilitate levelling up, then the joists on top of the beams. eg beams 4x2" laid side-on, joists 6X2" laid normal way up.
If there is a possibility of the underfloor getting wet, provide for many air vents. If the room were, for instance, 15ft wide, I would normally have three vents on each side of the house, but if there is a risk of damp, then five a side. One cannot really over-ventilate.
After building the sleeper walls, the underfloor should be covered with 2" of weak cement mix as an oversite. This will inhibit any soil damp.
It is quite possible to drill through the 18" walls, only needs 4" holes, then a grille on the outside. At least it is possible if the necessary skills are available locally.
Personally, I would not start taking stones out of the wall, that sounds a good way to damage it, unless it is ashlar and single stones can be removed cleanly. Is it lime mortar or cement?
Brittany, lovely. Used to go to Quiberon with my parents in the 60s. Over-run with tourists now, I suppose.
We visited Brittany in 2010 with a car club, stayed here
http://www.lecosquer.com/
Envy your friend.
Ivor
If there is a possibility of the underfloor getting wet, provide for many air vents. If the room were, for instance, 15ft wide, I would normally have three vents on each side of the house, but if there is a risk of damp, then five a side. One cannot really over-ventilate.
After building the sleeper walls, the underfloor should be covered with 2" of weak cement mix as an oversite. This will inhibit any soil damp.
It is quite possible to drill through the 18" walls, only needs 4" holes, then a grille on the outside. At least it is possible if the necessary skills are available locally.
Personally, I would not start taking stones out of the wall, that sounds a good way to damage it, unless it is ashlar and single stones can be removed cleanly. Is it lime mortar or cement?
Brittany, lovely. Used to go to Quiberon with my parents in the 60s. Over-run with tourists now, I suppose.
We visited Brittany in 2010 with a car club, stayed here
http://www.lecosquer.com/
Envy your friend.
Ivor
Good evening all and thank you to Keith for putting my question forward on my behalf.
I am in France in the building concerned have spent quite a lot of time undoing previous work by the former owners following advice I have been given.
I have just been next door to see what they have done to combat the flood issues in their place (their house is a holiday home so this is the first opportunity I have had to go inside) and they have told about the remedial work they made 20 years ago. In effect what they have done is to raise the floor above the previous flood levels but they got a local French Artisan to do the work. He dug out a load of the earth and then put a layer of compacted gravel down. On top of this he laid a solid concrete slab and then a layer of polystyrene insulation followed (I think) by a thin screed layer and clay tiles on top.
In the 20 years they have since had the house they have never had problems with "humidité" in the house. What I couldn't work out with my garbled french was whether there is a DPM layer or not. The problem is I am left with a predicament. Their house is testament to having been a successful solution to the flood (12 years ago it flooded badly and the garden was submerged which is a higher level than we saw the winter before last) and yet it would appear to fly in the face of all the advice I have read on this forum.
He was adamant that I should avoid timber and have a solid floor instead.
I have seen with my eyes the result, their house is dry and no hint of damp so I must consider what I have just been told but what is the view of the forum please?
Confused of Brittany!!
I am in France in the building concerned have spent quite a lot of time undoing previous work by the former owners following advice I have been given.
I have just been next door to see what they have done to combat the flood issues in their place (their house is a holiday home so this is the first opportunity I have had to go inside) and they have told about the remedial work they made 20 years ago. In effect what they have done is to raise the floor above the previous flood levels but they got a local French Artisan to do the work. He dug out a load of the earth and then put a layer of compacted gravel down. On top of this he laid a solid concrete slab and then a layer of polystyrene insulation followed (I think) by a thin screed layer and clay tiles on top.
In the 20 years they have since had the house they have never had problems with "humidité" in the house. What I couldn't work out with my garbled french was whether there is a DPM layer or not. The problem is I am left with a predicament. Their house is testament to having been a successful solution to the flood (12 years ago it flooded badly and the garden was submerged which is a higher level than we saw the winter before last) and yet it would appear to fly in the face of all the advice I have read on this forum.
He was adamant that I should avoid timber and have a solid floor instead.
I have seen with my eyes the result, their house is dry and no hint of damp so I must consider what I have just been told but what is the view of the forum please?
Confused of Brittany!!
88v8
Member
- Messages
- 3,131
- Location
- Glorious Gloucs
Hello and welcome.
The presumption in soggy old England is that the ground beneath the house will be damp.
There is also a presumption that there is a thing called 'Rising Damp' although this to a large extent depends on the brick/stone of which the house is built; some is more permeable than others.
A solid floor with dpm does not permit the evaporation of damp. Hence, damp arising beneath the floor will be pushed sideways until it reaches the wall, and will then rise up the wall - which in an old house will have no dpc - sometimes to a height of a few feet.
Thus, the default principle in an old English house is that it needs to breathe, so that the damp can be generally evaporated or ventilated away and does not concentrate in the structure.
However....
Albeit your house is intermittently exposed to flood, perhaps the underlying ground is not usually damp, hence there is no rising damp worth speaking of.
In that case, perimeter protection, walls without penetrations, and a solid floor, may be better than a suspended floor with vents which inevitably would take a while to dry after flooding.
Twenty years is long enough to prove what works or not.
In my house, a cement floor of 1972 with dpm made the perimeter and walls so damp that the Gripperods had rotted.
I took it up and put in a Limecrete floor without dpm, now the room is dry.
I do not think you would be doing anything detrimental by building a suspended floor, but the insertion of vents does make the underfloor more floodable, and if the water rises high enough to wet the floor, or stands there for an extended period, the floor will be damaged.
Every house is different and there is no point in flying in the face of what works. One cannot keep water out with dogma.
If your house is built of the same stone as next door's, sitting on the same sub-base, on the same level, then the same solution may be better, even though what you describe is simply a typical modern floor.
A thick (6" or more) gravel underlay would allow for a degree of ebb and flow in the ground water.
If I went that route, I would be sure to tie the dpm into the walls, otherwise floodwater could just come up around the edge.
It's hard, knowing what to do for the best. If one employs the average tradesman over here, he reaches for a bag of cement, which is absolutely inimical to most old houses, so one cannot always rely on the prevailing wisdom.
One point that might tip the balance is that if this is a holiday home, it would likely flood when you are not there, and one cannot actually damage a solid floor by flooding it.
Sorry to be vague. If you would like to post a few pics, it might help get a better feel.
Brittany... lovely... stayed near Guingamp a few years ago, and used to visit Quiberon in the 60s.
Ivor
The presumption in soggy old England is that the ground beneath the house will be damp.
There is also a presumption that there is a thing called 'Rising Damp' although this to a large extent depends on the brick/stone of which the house is built; some is more permeable than others.
A solid floor with dpm does not permit the evaporation of damp. Hence, damp arising beneath the floor will be pushed sideways until it reaches the wall, and will then rise up the wall - which in an old house will have no dpc - sometimes to a height of a few feet.
Thus, the default principle in an old English house is that it needs to breathe, so that the damp can be generally evaporated or ventilated away and does not concentrate in the structure.
However....
Albeit your house is intermittently exposed to flood, perhaps the underlying ground is not usually damp, hence there is no rising damp worth speaking of.
In that case, perimeter protection, walls without penetrations, and a solid floor, may be better than a suspended floor with vents which inevitably would take a while to dry after flooding.
Twenty years is long enough to prove what works or not.
In my house, a cement floor of 1972 with dpm made the perimeter and walls so damp that the Gripperods had rotted.
I took it up and put in a Limecrete floor without dpm, now the room is dry.
I do not think you would be doing anything detrimental by building a suspended floor, but the insertion of vents does make the underfloor more floodable, and if the water rises high enough to wet the floor, or stands there for an extended period, the floor will be damaged.
Every house is different and there is no point in flying in the face of what works. One cannot keep water out with dogma.
If your house is built of the same stone as next door's, sitting on the same sub-base, on the same level, then the same solution may be better, even though what you describe is simply a typical modern floor.
A thick (6" or more) gravel underlay would allow for a degree of ebb and flow in the ground water.
If I went that route, I would be sure to tie the dpm into the walls, otherwise floodwater could just come up around the edge.
It's hard, knowing what to do for the best. If one employs the average tradesman over here, he reaches for a bag of cement, which is absolutely inimical to most old houses, so one cannot always rely on the prevailing wisdom.
One point that might tip the balance is that if this is a holiday home, it would likely flood when you are not there, and one cannot actually damage a solid floor by flooding it.
Sorry to be vague. If you would like to post a few pics, it might help get a better feel.
Brittany... lovely... stayed near Guingamp a few years ago, and used to visit Quiberon in the 60s.
Ivor
Flyfisher
Member
- Messages
- 10,168
- Location
- Norfolk, UK
I'm just thinking out loud here (a dangerous thing to do) but is there any place for a suspended solid floor in these circumstances?
If the final floor is to be tiled then a solid floor is an advantage. Combine this with an underfloor void and it provides ventilation around the footings of the existing walls, which is generally a good thing. Plus, with no need to be breathable, a cement construction would not be problematic. The final construction would also be rot-proof, unlike a timber suspended floor, which would be a useful consideration if prone to flooding.
Probably a daft idea, though I can't immediately see why. Didn't Feltwell do something similar with his rather fabulous garage?
Something like the 'suspended concrete' option here: http://www.homebuilding.co.uk/advice/key-choices/foundations/floor-structure-guide
More info here: http://www.supremeconcrete.co.uk/general/suspended-beam-and-block-floors/
If the final floor is to be tiled then a solid floor is an advantage. Combine this with an underfloor void and it provides ventilation around the footings of the existing walls, which is generally a good thing. Plus, with no need to be breathable, a cement construction would not be problematic. The final construction would also be rot-proof, unlike a timber suspended floor, which would be a useful consideration if prone to flooding.
Probably a daft idea, though I can't immediately see why. Didn't Feltwell do something similar with his rather fabulous garage?
Something like the 'suspended concrete' option here: http://www.homebuilding.co.uk/advice/key-choices/foundations/floor-structure-guide
More info here: http://www.supremeconcrete.co.uk/general/suspended-beam-and-block-floors/
Apologies for being unable to post photos but my internet connection is dreadfully slow.
I have reached the stage of laying down my hard core base. I have some old concrete blocks left over from demolishi g a wall and I am tempted to use them. However, I pondered the idea and thought I might be better off using stone instead. My thinking is that in times of high water levels I should be looking for materials that will drain quickly. It will be under a moisture barrier but nevertheless I should imagine the concrete blocks broken into rubble will retain moisture for longer.
Would others agree?
We are further south from where you stayed. We are in Malestroit. Look up Malestroit inondations on youtube to see what the river does i flood!
I have reached the stage of laying down my hard core base. I have some old concrete blocks left over from demolishi g a wall and I am tempted to use them. However, I pondered the idea and thought I might be better off using stone instead. My thinking is that in times of high water levels I should be looking for materials that will drain quickly. It will be under a moisture barrier but nevertheless I should imagine the concrete blocks broken into rubble will retain moisture for longer.
Would others agree?
We are further south from where you stayed. We are in Malestroit. Look up Malestroit inondations on youtube to see what the river does i flood!
88v8
Member
- Messages
- 3,131
- Location
- Glorious Gloucs
Sorry, didn't see your query earlier...
If they are solid concrete (as opposed to clinker) I think there would be little difference from stone. The moisture retention would be determined by the particle size - smaller pieces of stone or block would hold more water.
Ivor
If they are solid concrete (as opposed to clinker) I think there would be little difference from stone. The moisture retention would be determined by the particle size - smaller pieces of stone or block would hold more water.
Ivor