conservatory

[vibetime]

Hi all,
i am planning to build my own conservatory, and have a few questions regarding this. i have looked on the net but am struggling for answers.

1- it will have two walls of a single course of bricks (full glass pannels)and one wall will be block external and lightweight block internal, (full height wall) does the cavity need backfilling with conrete between the blocks below dpc ? if so why ?

2 - i will be using a waterproof wool type cavity insulation, and leaving an air gap, does this insulation need to sit just off the footings, to prevent damp rising, or just start upwards of dpc ?

3- does the insulation need to be touching the internal blocks but not the external ,so to avoid moisture bridging?

[welsh brickie]

the cavity needs filling with weak concrete up to 2 bricks below your dpc because of external pressure from the ground,alternatavly you can use trench blocks.

Cavity insulation sits on the wall ties at dpc height

the insulation sits tight against the inner leaf of brickwork and is held back away from the outer blockwork using plastic discs that clip onto the wall tie

[vibetime]

thanks for your reply. what is the mix for weak concrete ? been told to mix my footings at 5 parts ballast to 1 part cement ?
also what size cavity should i have ?
i dont need building regs but i want to do it to a good standard and i have read i need an air gap between the cavity insulation and the external blocks.

[vibetime]

thanks for your reply.
what is the minumun cavity i can get away with ? dont need regs but want to do it right.
if i use trench fill to roughly 150mm below ground level, i guess i would not need to part fill the cavity to 2 courses below dpc ?

[welsh brickie]

If you want minimum cavity you can keep it 50mm and use drytherm full fill cavity bats,No airgap and its water resistant.Or go 75mm with a 25mm airgap or 100mm cavity with 50mm insulation and 50mm air gap.

Trench blocks are made of thermalite and are 300mm wide so eliminates the use of cavity fill.

Concrete for the cavity fill is 12 balast to 1 cement if you want to do inner and outer leafs of blockwork,Its weak so there is little expansion in the concrete when it sets

[vibetime]

thanks for your help, its appreciated. its cleared alot up.

[vibetime]

another question !
minimum widths for footings that are trench fill
is it the width thats most important ? as it spreads the load out ?
do i need to go 600 wide with it just been a cony?
two walls are only single brick , i had planned on a 300 wide trench for these, is that enough ?
thanks.

[welsh brickie]

you need 600mm wide foundation the wall thickness minimum you want is 100mm brick 50mm cavity and 100mm block giving an overall wall thickness of 250mm.On the foundation you need a 150mm toe of concrete each side of the wall this spreads the weight of compression on the foundation.This is standard...Remember its the weight of the wall and the conservatory.

[vibetime]

just to clarify, a 600 wide trench for the cavity wall side of the cony, but the other two walls wont have a cavity as there full height glass pannels and only sit on one brick (about five courses high), so do these still need a 6oo wide trench ? its just alot more digging as im down to 800 deep at moment and have just hit decent ground, so it will be a fair amount of concrete to fill em if they also need 600 width rather than the 3- 400 i have now.
thanks once again.