Lean to Garden Room Concrete Base Air Brick query

[LGWIZZ]

Hi All, Hope you are well, we have recently purchased a property and currently putting some plans in place. One thing we will be doing is putting a addroom on the back (a lean to garden room attached to the house. However i have a dilemma with the air bricks of the original house. In usual extensions we would obviously build foundations brick up and run a air vent extension across. However in this situation we just require a 100mm Concrete pad on top of compacted type 1. I plan to have the concrete pad slightly above ground level but how could i extend the air bricks? Would i be able to extend under the concrete base and fix the vent to the front face of the pad? The other option i have thought of is to put in aco drain at the back of the bad and build the addroom on top as it sits on 4 x 2 treated timber batten. but would this be enough air flow under? Thankyou in advance.

 

[LGWIZZ]

Any Advice please?

 

[Deluks]

You can extend the air brick under the pad using a periscope vent at each end. The other bit about an Aco drain is not very clear.

 

[LGWIZZ]

Hi Deluks Thanks for your reply. This was my plan but usually there is a course of brickwork that the vent then connects to, there will be no brick course on this pad as it does not require foundations or brick work. So could i concrete over the periscopes and where the extended periscope comes up in the concrete could the vent just sit in the concrete pad if its above ground level?

 

[Deluks]

There's no reason why you can't built the periscope into the concrete pad, with care though as it might get moved, or damaged with a shovel.
Perhaps build some shuttering around it until pour is complete, let the concrete firm up for a short while, then remove the shuttering and shovel more concrete around it, but whilst the concrete is still wet so it all bonds together.

What is this garden room made from? Presumably it has a built in floor and its own DPC?

 

[^woody^]

Periscopes at each end can lead to water holding in the duct pipe. Normally you would knock a new hole in the house at lower level, angle the duct pipe slightly, and periscope at the outer end.

It may be better if the new outer air bricks are formed in the new structure and then ducted down and then horizontally under the slab

It all really depends on the structure and slab detail.

Bear in mind that length of ducting and angles can reduce air flow, so would larger ducts or more of them be required to compensate?