Extension advice please

[mountdale]

Hi
I am new here and just wondered if anyone could give me some advice on building a single storey L shaped extension onto the back of my existing property.

1) firstly the damp course is about 6 courses up from the ground on my existing build, so my first question is do i fill my footings right up with concrete or do i need to leave it just short at the top. I guess it can come right to the top as there is as i say about 6 courses of brickwork to build up to damp course?

2) to bring it upto damp (and also the extising joing floor level almost), can i assume that i just build the courses as complete rows, i.e do not build the peers yet for where the french doors will be put?

3) after completing the above (two skins) should i maybe fill the cavity with concrete? I was just thinking ahead of when i put the doors in so that there isn't a cavity underneath the door cill?

4) When building around the door/window openings (peers), how much gap should i leave in relation to the size of the actual door/window frame?

Many Thank for any help offered.

 

[noseall]

[quote="mountdale";p="1121119"

1

) firstly the damp course is about 6 courses up from the ground on my existing build, so my first question is do i fill my footings right up with concrete or do i need to leave it just short at the top. I guess it can come right to the top as there is as i say about 6 courses of brickwork to build up to damp course?

make sure you make allowances for any drain gullies or rest bends. personally i would keep the foundation top 300mm (min) down from the ground level.

2) to bring it up to damp (and also the extising joing floor level almost), can i assume that i just build the courses as complete rows, i.e do not build the peers yet for where the french doors will be put?

correct. it pays to have a single engineering brick finishing course (as opposed to a full block) ,on the internal skin, as you may need to remove this brick later on to allow the finished floor to carry on up to the doors.

3) after completing the above (two skins) should i maybe fill the cavity with concrete? I was just thinking ahead of when i put the doors in so that there isn't a cavity underneath the door cill?

the cavity is filled to within 225mm of the damp course, only complete it as such. if you fill it any higher the b.c.o. will ask you to remove it! when it comes time to making good the cavity section where any doors may be then use a little patience. assuming a door position at the footings stage can be dangerous as the facing brick sizes may differ above d.p.c. and can result in an altered door position.

4) When building around the door/window openings (peers), how much gap should i leave in relation to the size of the actual door/window frame?

do you have the frames already?
Many Thank for any help offered.[/quote]

 

[iaink]

go to "your projects" in this forum
go to extension

p.s only fill your cavity to ground level.

 

[noseall]

p.s only fill your cavity to ground level.

a little bit ambiguous i think, as g/l can vary.

up to within 225mm of dpc is acceptable.

don't forget, as well as external ground pushing in there will be oversite in-fill pushing out.

lean mix cavity fill to within 225mm.

edit to add: you never know when the ground level might need to be raised. try filling the cavity then!

 

[mountdale]

[Quote:
4) When building around the door/window openings (peers), how much gap should i leave in relation to the size of the actual door/window frame?
do you have the frames already?
quote]


Hi Noseall,
Thanks for that.
Yes i do already have the window. It measures 2032mm wide and 1235 mm high. I have already got the doors for when i start, but not here yet so cannot confirm the sizes.[/quote]

 

[mountdale]

1Quote:
) firstly the damp course is about 6 courses up from the ground on my existing build, so my first question is do i fill my footings right up with concrete or do i need to leave it just short at the top. I guess it can come right to the top as there is as i say about 6 courses of brickwork to build up to damp course?
make sure you make allowances for any drain gullies or rest bends. personally i would keep the foundation top 300mm (min) down from the ground level.

Thanks - makes sense

Quote:
2) to bring it up to damp (and also the extising joing floor level almost), can i assume that i just build the courses as complete rows, i.e do not build the peers yet for where the french doors will be put?
correct. it pays to have a single engineering brick finishing course (as opposed to a full block) ,on the internal skin, as you may need to remove this brick later on to allow the finished floor to carry on up to the doors.

when this is all done, then i can introduce the returns(i.e a brick coming across the cavity and onto the internal skin?)

Quote:
3) after completing the above (two skins) should i maybe fill the cavity with concrete? I was just thinking ahead of when i put the doors in so that there isn't a cavity underneath the door cill?

the cavity is filled to within 225mm of the damp course, only complete it as such. if you fill it any higher the b.c.o. will ask you to remove it! when it comes time to making good the cavity section where any doors may be then use a little patience. assuming a door position at the footings stage can be dangerous as the facing brick sizes may differ above d.p.c. and can result in an altered door position

i assume this to be just a normal wet concrete mix that i can pour into the cavity over maybe some hardcore? Then when i start beuilding the remainder of the skins the insulation will sit inside the skins and on top of the aforementioned concrete?
I thought perhaps also, before building the lower inner skin and filling with concrete i should maybe paint some bitchomin on the inside of the outer skin to as further damp protection. I am just trying to recall some of the procedures that Building Regs asked/requested last time.
Thanks again.

 

[noseall]

Yes i do already have the window. It measures 2032mm wide and 1235 mm high. I have already got the doors for when i start, but not here yet so cannot confirm the sizes.

[/quote]

3mm up each side - 6mm in total.

 

[mountdale]

Hi Noseall,
Thanks for all your help so far. I am having trouble replying in the same neat manner as you do! I have underlined my original question, and put your expert replies so far in italics. Sorry to ask so many simple questions but just like to check to refresh my memory!

2) to bring it up to damp (and also the extising joing floor level almost), can i assume that i just build the courses as complete rows, i.e do not build the peers yet for where the french doors will be put? correct. it pays to have a single engineering brick finishing course (as opposed to a full block) ,on the internal skin, as you may need to remove this brick later on to allow the finished floor to carry on up to the doors.

when this is all done, then i can introduce the returns(i.e a brick coming across the cavity and onto the internal skin?). Also, can the internal skin upto damp be built using block work with the single engineering brick finishing course or does it all need to be brick?

3) after completing the above (two skins) should i maybe fill the cavity with concrete? I was just thinking ahead of when i put the doors in so that there isn't a cavity underneath the door cill?
the cavity is filled to within 225mm of the damp course, only complete it as such. if you fill it any higher the b.c.o. will ask you to remove it! when it comes time to making good the cavity section where any doors may be then use a little patience. assuming a door position at the footings stage can be dangerous as the facing brick sizes may differ above d.p.c. and can result in an altered door position

i assume this to be just a normal wet concrete mix that i can pour into the cavity over maybe some hardcore? Then when i start beuilding the remainder of the skins the insulation will sit inside the skins and on top of the aforementioned concrete?
I thought perhaps also, before building the lower inner skin and filling with concrete i should maybe paint some **** on the inside of the outer skin to as further damp protection. I am just trying to recall some of the procedures that Building Regs asked/requested last time.

4)3mm up each side - 6mm in total

would this be 3mm at the top as well?

 

[noseall]

all masonry below dpc can be built in either 7n dense concrete blocks or class b semi-engineering bricks or similar ffl grade.

i mentioned finishing the internal leaf with a single brick course for practicality as this brick can be easily removed when it comes time for bridging the cavity with the floor screed. if however you were installing an all-in-one troweled concrete slab then it would make sense to define the openings below dpc level.

openings can be defined above dpc by bridging the cavity with a piece of block and vertical dpc. these days however we don't tend to close the cavity with masonry but simply build the openings with a stopped block without the return. the cavity is then filled with proprietary cavity closers.

the cavity (below dpc) is filled with lean mix concrete. it is simply to stop the forces of soil and oversite (hard core etc) pushing on the leaves of masonry. mix it 8:1 max. no need for hard core.

by keeping the cavity fill 225mm down from the dpc you effectively form a trough. this trough can deal with any unwanted moisture. it is advisable to cut cavity batts and place them in the trough prior to starting the above dpc build. do not let any insulation go past dpc as this will mess up the ties. start with a tie wire on the dpc and work up from there.

no need for any paint.

3mm up each side of the door or window and allow 10mm for height as this will be taken up with a mortar bed, foam or silicone.