Subfloor ventilation

[Michaelsf90]

Does anyone know the recommended number of brick vents usually required? House is a 1930s semi. There are two on the front in the bay window. One on the side towards the front end. A small utility room extension has been built so I don't know if ones has been covered. The back end of the house doesn't have a vent on the side. Their is one on the back. So in total two on the front. One on the side and one on the back. Nothing flagged up on the survey

 

[KenGMac]

Michaelsf90, good evening.

As a general rule of thumb an air brick every 1.5 to 2.5 m should be OK

But it all depends on the overall total "footprint" of the property.

There is a very high probability that the retro-build rear extension has blocked of at least one vent, it costs to ensure that the original air brick on a rear wall is carried on under an extension, the extension of an air brick is not rocket science?

Does the rear extension have a solid floor or is the floor suspended?

As you have access to the "side" of the house you can happily introduce more vents in this elevation?

As an aside? why do you need more ventilation underfloor??

As a second aside is there any access under the floor? to allow you to see the rear wall from the inside, and ??? possibly introduce some under floor insulation??

Ken.

 

[Michaelsf90]

The house is 6m wide by 8m long. Front is 6. Back is 6. Side is 8. The front has two that are in the bay window and probably 1 metre apart. None in the porch. One on the side about a metre from the front. The utility room is on the side. Like you said that probably covers one. On the back their is one which looks like it goes under the kitchen. Their isn't one in the back going under the front room. I have been under the floor. Smells damp but as an electrician I've been under many and they all smell damp. It certainly felt very draughty. The utility room will be a concrete floor as it's only a few years old. I'm just asking out of interest. I'd sooner know it's right

 

[Leofric]

Air bricks nearer to 1.5m crs than 2.5m ! Should provide cross ventilation to the sub floor. A new concrete floor should have had ducting to provide ventilation through to the sub floor from air bricks.

 

[Michaelsf90]

These are the two at the front and one at the back

 

[Michaelsf90]

Two at the front and one at the side. Sorry

 

[KenGMac]

Michaelsf90, good evening.

OK I am now confused, no a rare occurrence.

in one of the images posted there are indeed 2 air bricks, but they appear very close together and at differing levels, are these the 2 at the front?

Ken

 

[Michaelsf90]

The one higher up I'm guessing is for air flow in the cavity wall. If you look carefully there is one to the left of the one at the bottom. Still very close together tho

 

[KenGMac]

Michaelsf90, good evening again.

As a general rule cavities should not have an air flow, any large air flow will reduce the ability of the cavity to assist in keeping the property warm, a static un-vented cavity will keep the property warmer than a cavity with a howling gale passing through it?

To allow air bricks to function as intended the air bricks should be spaced out along any elevation and around the entire property, for example having three air bricks within 2 meters of each other on a gable measuring [say] 10 / 15.m does nothing at all for underfloor ventilation.

Another consideration is the underfloor compartments where the dwarf walls criss cross the property and are there to support the timber floor joists, these walls are honeycombed, not solid so there is a slow air flow between the various compartments under floor

In my opinion you need to locate the underfloor areas and introduce at least one air brick into each.

Ken

 

[Michaelsf90]

Thank you ken. Where the two are on the bay window is one area. Dwarf walls along there with lots of holes in between the bricks. The hall looks to have the one air brick on the side and the kitchen has one on the back