Cavity Wall - Is it a cavity from the ground floor to the roof line?

[Scared_of_Dust]

Hello,

I need to improve the sub floor ventiulation (suspended timber) since the sub floor gets a few inches of water underneath after heavy rain due to the water table height.

In the past there was air vents at the front and rear of the property. But 20 years ago (and long before I owned the house) and extension was slapped on the back and side of the house.

As a result there is only airvents at the front at ground level.

Can I install air vents at the side of the house above the exntension and will this help with airflow from the ground level at the front to the side of the house approximately at first floor level - OR is there a break in the cavity between ground floor and first floor.

I hope that makes sense.

Dust

 

[KenGMac]

Scared_of_Dust, good evening.

Is the floor in the rear / side extension solid [concrete] or suspended timber and joists?

What age is the property? and are the external walls a timber framed construction or "traditional" cavity brick? and has that cavity been retro-filled with Insulation?

In general, the cavity should not be vented, it should be a sealed area, similar to a double glazed window unit, a sealed cavity assists with heat retention

In a timber frame there can be at times fire breaks installed at floor level which will prevent air flow between ground and first floor areas of cavity.

How much "crawl" space is there under the floors of the original property?

Sorry for all the questions but a picture needs to be established of the construction before any meaningful answers can be suggested

Ken

 

[Scared_of_Dust]

The property is circa 1963.

External walls are traditional cavity brick. Both the side and rear extention that has now blocked the air bricks are concrete based and so cannot be vented.

The crawl space is about 2 feet give or take. There is no cavity wall insulation.

I'm just thinking of ways to make the sub floor breath since it can't do so very effectively at the moment and the timber moisture level is a little higher than ideal (15-18% in places, about 10 in others).

I am installing a french drain at the front of the property that will go into my drain to help with the water when it rains - good idea or bad.

Honestly everyone I've spoke to has said a different thing. I am super confused.

Thank you for your guidance.

Dust.

 

[stuart45]

There should have been airbricks and ducts through the concrete floors of the extension to keep the old floor well vented. Putting airbricks above the extension won't help.

 

[KenGMac]

Scared_of_Dust, good evening, again.

OK, if you opt to use the cavity to route some sort of ventilation outlet "around" the concrete floor of the conservatory, you run the very high "probability" of introducing damp and at times moist air into the cavity + the probability of mould growth within the cavity, must admit the option is novel but has several down sides, [loss of thermal protection] [mould growth in the cavity]

How about considering using say 150.mm plastic drain pipes, hang them from the joists, and with open ends internally then using a bend, the pipe can be used as a conduit to the fresh air via an air brick?

OR? using a length of "flexible" duct, the sort of flexible ducting used for [exactly that purpose] moving air, as above. lead the flexible pipe to an air brick on an external wall close to the rear extension.

The latter [flexible] option would be far easier to install, easy to get into place albeit, it would entail you crawling around under the floor???

The rational is that if you have a pipe sited centrally[or so] along the length of the extension you can "induce" an air flow?

Just a consideration.

Ken.