Small extension enquiry

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Dear all,

I would greatly appreciate some assistance with the following enquiry which will help to shape my proposal prior to commissioning the services of my local builder.

I am considering having a small extension built to my property. The property is a small 3 bedroom detached house, built in the 1960’s. The house has double skinned external walls with imperial bricks and breeze blocks. The internal walls are breeze blocks. The entrance door is on the side of the house which is separated from the adjacent houses by concrete driveways.

The house has only one toilet in the upstairs bathroom and would be greatly enhanced by an occasional downstrairs toilet with basin and maybe a downstairs shower room.

To address this, some years ago, the property adjacent to ours had a simple, one story extension built into their driveway. The builder appears to have done a good job, however, this type of extension moves the front door from the position on the existing outer skin into the driveway thereby reducing the width of the driveway for the length of the extension. I am considering having a similar extension but am looking for ways of reducing the depth of the extension into the driveway.

I would greatly appreciate it if you could provide some guidance on the following:-

1. Considering that the existing outer double skinned wall would be retained and therefore become a new double skinned internal wall, would the new outer wall have to be double skinned? Please note that the toilet with basin/shower would be for occasional use. Heating in the extension would be either electric or water type underfloor heating. If the new outer wall had to be double skinned please can you advise on any known methods to reduce the wall thickness. For example, perhaps there is a very desnse plasterboard available which can be considered a second skin.
2. Could the extension be made from so called ‘slip bricks’ to reduce wall width.
3. There is an existing manhole cover in the driveway which appears to be an inspection cover or rodding point for my toilet pipework. It only serves my property. Could this cover be ‘removed’ or permanently sealed to allow the extension to be built over it? Please note there is a second cover ‘downstream’ of the first cover.
4. Prior to undertaking the extension, could I remove the existing outer skin of brick at ground level and insert a lintel to support the brickwork above. The fitment of the extention would then ensure that the brickwork that was removed would then be an interior wall.

Your initial thoughts on the above would be greatly appreciated.

Kind Regards





Paul
 
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Removing the outer skin of a side wall,and inserting a beam above, is an accepted way of gaining a few extra inches in width.

As regards your new outer wall; if built of brick/block with cavity fill, it will be around 285mm thick (exc. plaster).. If you had a brick outer skin, and 4x2 studwork for the inner leaf,(with insulation between the studs) you can get away with a 25 cavity, giving a wall thickness of 225 (exc. plaster).
You might be able to use 3" deep studs, with only 3" thick insulation board, if you put more insulation in the roof to compensate.

Is it possible to incorporate your front door within this extension in some way? (eg with separate door to the wc). It might then be classed as a porch and these are exempt fom Building Control.
 
thanks for the response and greatly appreciated. I am unsure yet as to whether I could effectively call / design the extention as a porch.

Do you think it may be possible to have thinner bricks to form the outside skin (I believe they are called slip bricks), again with batterning and insulation with no block inner skin. I will have substamtial room in the room for insulation
 
Removing the outer skin of a side wall,and inserting a beam above, is an accepted way of gaining a few extra inches in width.

As regards your new outer wall; if built of brick/block with cavity fill, it will be around 285mm thick (exc. plaster).. If you had a brick outer skin, and 4x2 studwork for the inner leaf,(with insulation between the studs) you can get away with a 25 cavity, giving a wall thickness of 225 (exc. plaster).
You might be able to use 3" deep studs, with only 3" thick insulation board, if you put more insulation in the roof to compensate.

Is it possible to incorporate your front door within this extension in some way? (eg with separate door to the wc). It might then be classed as a porch and these are exempt fom Building Control.



Tony, would the second option ie brick and studwork provide the same level of insulation as a block/brick cavity wall?

Thanks
 
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Tony, would the second option ie brick and studwork provide the same level of insulation as a block/brick cavity wall?

Thanks

Indus; probably not, though not far short. For a brick/50mm cavity/ 4x2 studs with 80mm Kingspan Kooltherm K17 board/12.5mm plasterboard and skim, you get 028. Without doing the calcs, I would guess the wall I suggested would probably give around 0.3 / 0.32; thats why he'd need a little more insulation in the roof to compensate.
 
tony, what are your thoughts on the slip brick question I raised
 
thanks for the response and greatly appreciated. I am unsure yet as to whether I could effectively call / design the extention as a porch.

Do you think it may be possible to have thinner bricks to form the outside skin (I believe they are called slip bricks), again with batterning and insulation with no block inner skin. I will have substamtial room in the room for insulation

Brick slips, although thin, are not intended for applications such as yours where space is limited. They are primarily intended for gluing on to a solid substrate (such as a concrete beam) when a brick-like appearance is required.
 
OK toni, so it looks like something I should be going for is a single brick, with battens, insulation and then a quality plasterboard. Then a shedload of insulation in the roof??
 
[



Tony, would the second option ie brick and studwork provide the same level of insulation as a block/brick cavity wall?

Thanks

Indus; probably not, though not far short. For a brick/50mm cavity/ 4x2 studs with 80mm Kingspan Kooltherm K17 board/12.5mm plasterboard and skim, you get 028. Without doing the calcs, I would guess the wall I suggested would probably give around 0.3 / 0.32; thats why he'd need a little more insulation in the roof to compensate.


Tony, just so I'm clear about what we are talking about. On one hand we have the usual outer brick, cavity stuffed with insulation and then blockwork wall. Then there is the other you mentioned. Is that basically outer brickwork with 3-4'' battens/studs straight onto and the spaces stuffed with insulation and then plasterboard as the final layer?


Paul, I hope you don't mind me hijacking the thread just to clarify this point.
 
no problem indus, tony if you could help that would be appreciated
 
[



Tony, would the second option ie brick and studwork provide the same level of insulation as a block/brick cavity wall?

Thanks

Indus; probably not, though not far short. For a brick/50mm cavity/ 4x2 studs with 80mm Kingspan Kooltherm K17 board/12.5mm plasterboard and skim, you get 028. Without doing the calcs, I would guess the wall I suggested would probably give around 0.3 / 0.32; thats why he'd need a little more insulation in the roof to compensate.


Tony, just so I'm clear about what we are talking about. On one hand we have the usual outer brick, cavity stuffed with insulation and then blockwork wall. Then there is the other you mentioned. Is that basically outer brickwork with 3-4'' battens/studs straight onto and the spaces stuffed with insulation and then plasterboard as the final layer?


Paul, I hope you don't mind me hijacking the thread just to clarify this point.
 
Thanks Tony, great drawing!

I see the insulation fills the width of the timber, do you put insulation in the cavity as well?

Thanks again
 
OK toni, so it looks like something I should be going for is a single brick, with battens, insulation and then a quality plasterboard. Then a shedload of insulation in the roof??

Does the extension need to be faced with brick? Could you build the external wall in 4x2 studwork with insulation within it, then clad with OSB, tyvek, battens and cedar cladding, in that order? That would save you a couple of inches.

I built a porch this way (exempt from BR), but I'm not conversant with the U-value calculations. I'm a DIYer not a builder, so perhaps a builder can comment on whether this is appropriate.

Cheers
Richard
 

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