Any builders out there? Cavity wall question.
Discussion
The thickness of the external walls depend on how you decide to insulate the wall to achieve the required U value. It is usual to have a 100mm outer skin (brickwork or rendered blockwork) the size of the cavity and the inner skin then depends upon whether you will be using insulating inner blocks or placing insulation in the cavity (or a combination of both).
It is usual for the wall between a garage and habitable room to be of cavity construction but it is by no means a specific requirement. It again comes down to achieving the correct U values, this can sometimes be attained by dry-lining.
It is usual for the wall between a garage and habitable room to be of cavity construction but it is by no means a specific requirement. It again comes down to achieving the correct U values, this can sometimes be attained by dry-lining.
I'm an Architect, not a builder, but if you want a 'typical' thickness for a cavity wall, about 300mm is near enough for the purposes of a drawing.
Outer leaf (brickwork) is nominally 102mm.
Cavity will vary between 50mm and about 95mm, depending upon type of insulation.
Inner leaf will be 100mm blockwork in most instances.
Finishes to inner face either plaster (12.5mm nominal thickness) or dry lining (say 25mm overall thickness, depending on method of fixing).
There is no specific requirement for walls between garages and habitable rooms to be cavity construction, as Boxbrush says. They are regarded as 'semi-exposed' (that is to say, the unheated space on the garage side is deemed to provide some level of reduction in heat loss by itself), so have a lower U-value requirement. Personally, I wouldn't normally use cavity construction, but a cavity wall would give better insulation and better sound reduction, at an increased cost.
E-mail me off list if you require further, specific advice.
Without wishing to sound discouraging though, you need to bear in mind that there are fairly complex Buidling Regulations requirements (eg. on heat loss - which will dictate precise wall construction and thickness more than anything else), so if you are having to ask such basic questions, you might be better off investing £600-£700 in a set of plans from someone who does 'PJ's' on a night to supplement their income!
>> Edited by Martin_S on Wednesday 3rd November 19:10
Outer leaf (brickwork) is nominally 102mm.
Cavity will vary between 50mm and about 95mm, depending upon type of insulation.
Inner leaf will be 100mm blockwork in most instances.
Finishes to inner face either plaster (12.5mm nominal thickness) or dry lining (say 25mm overall thickness, depending on method of fixing).
There is no specific requirement for walls between garages and habitable rooms to be cavity construction, as Boxbrush says. They are regarded as 'semi-exposed' (that is to say, the unheated space on the garage side is deemed to provide some level of reduction in heat loss by itself), so have a lower U-value requirement. Personally, I wouldn't normally use cavity construction, but a cavity wall would give better insulation and better sound reduction, at an increased cost.
E-mail me off list if you require further, specific advice.
Without wishing to sound discouraging though, you need to bear in mind that there are fairly complex Buidling Regulations requirements (eg. on heat loss - which will dictate precise wall construction and thickness more than anything else), so if you are having to ask such basic questions, you might be better off investing £600-£700 in a set of plans from someone who does 'PJ's' on a night to supplement their income!
>> Edited by Martin_S on Wednesday 3rd November 19:10
simpo two said:
I think that you also need a wall/door between the garage and house that's up to a certain fire rating - in case your petrol tank explodes...
...and, unless you are disabled and have a very sympathetic Building Control Officer, there has to be a minimum threshold at the door, to prevent any flamable or noxious liquids flowing back into the habitable part of the property if they spill.
Really...there are so many regulations and practical technical requirements, many of them not at all obvious, that you would be daft to try and crate a set of drawings yourself unless you are pretty clued up. Do yourself a favour - get a professional involved!
Martin S and everyone - thanks for the replies.
Re-reading my post I realise it may look like I'm doing the job myself, nothing further from the truth. The extent of my handiwork is cutting the grass
No, the idea is for me to sketch a floor plan of the existing place and try various alternatives as to what would work best, then get the pro's in to discuss further and actually do the job properly.
I needed the cavity size so I could draw pretty much to scale to see what the room sizes would be in the various configurations.
Thanks again.
PS Simpo - if the wife every left any bloody fuel in the car I would be worried about the regs for fire doors
Re-reading my post I realise it may look like I'm doing the job myself, nothing further from the truth. The extent of my handiwork is cutting the grass
No, the idea is for me to sketch a floor plan of the existing place and try various alternatives as to what would work best, then get the pro's in to discuss further and actually do the job properly.
I needed the cavity size so I could draw pretty much to scale to see what the room sizes would be in the various configurations.
Thanks again.
PS Simpo - if the wife every left any bloody fuel in the car I would be worried about the regs for fire doors
If the garage is being built against an existing wall then it will most likely already be a two skin cavity wall (most are since about 1920s). You would therefore need double skins to support the brickwork above.
With regard to the door between the house and the garage, it will need to be half hour fire rated. Nothing in a normal two storey hous needs to be rated at more than half hour.
This can be achieved using a quite lightweight door but you have to consider that your garage door won't pose much of a problem to a burglar. Once in your garage he can then work on this door with some impunity. So you want a very strong door and frame here.
If you have any other queries then mail me and if you are in the Beds Herts area I can recommend a couple of Architects who do PJs.
With regard to the door between the house and the garage, it will need to be half hour fire rated. Nothing in a normal two storey hous needs to be rated at more than half hour.
This can be achieved using a quite lightweight door but you have to consider that your garage door won't pose much of a problem to a burglar. Once in your garage he can then work on this door with some impunity. So you want a very strong door and frame here.
If you have any other queries then mail me and if you are in the Beds Herts area I can recommend a couple of Architects who do PJs.
Cheers RSV, although I'm in Hampshire.
I plan to have built a single storey side extention, firts room out would be an office and next the garage, I take your point about a burgler I plan on having a super tough garage door and no windows in there at all.
20,000,000 volts to the door and surround to the inner door should keep the most determined pikey at bay
I plan to have built a single storey side extention, firts room out would be an office and next the garage, I take your point about a burgler I plan on having a super tough garage door and no windows in there at all.
20,000,000 volts to the door and surround to the inner door should keep the most determined pikey at bay
Martin_S said:
there has to be a minimum threshold at the door, to prevent any flamable or noxious liquids flowing back into the habitable part of the property if they spill.
True - my mother's house (with integral garage) was built in 1987 and has a step of about 2" down into garage. And the fire door is a heavy spring-loaded one. It also has a decent lock on it, so that if a burglar manages to open the up-and-over garage door, he can't just walk into the rest of the house.
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