Under Floor Ventilation

[Jud234]

I am currently in the process of building an extension. The base is concrete. Following an building inspection it has been identified that there is no under floor ventilation to the already existing house. The ventilation was not on the plans, other inspection from building controls at various stages did not identify this, and the plans were approved by building controls.

What do I do ?

1) Can I add extra ventilation from the side of the house ? If so how many point of ventilation are required and from which direction ?
2) Can I ventilate into the next door neighbours under floor ventilation.

or is the only option digging up the base ?

 

[Static]

What flooring does the existing house have?
How large?
what foundations?
what void under floor?
how old is the house?
is there a DPC?
how big is the new extension?
does the new extension have a void under the floor?
what type of soil are you founding on?
are you putting in any underfloor ventilation to the new extension?
what area of the country to you live in?

Little more info please..

 

[Jud234]

The floor in the existing house is suspended wooden floor, and was built in 1930,s. As far as I am aware the original building has a DPC.

The extension is across the width of the house (approx 3x5.7m) and does not have a void under the flloor.

I am from South Yorkshire.

 

[Static]

Ok, you should put in air bricks to ventilate the void below the existing wooden flooring. Chances are that it has already rotten the joists over the last 80 years so you may also need to replace some of the joists. Installing air bricks is a fairly painless experience but will require the internal boards are lifted and which they are up the joists can be checked.
Oh and you cant ventilate into next doors property.

 

[Jud234]

Thanks, can I ventilate from the side as the concrete base from the extension is already laid. If so how many points of ventillation ?

 

[Static]

Hmm, aim for 500mm^2 for every m^2 of flooring. So youll probably end up with an airbrick every 1200mm or so. All timber floors should be ventilated on at least 2 opposite sides. Openings made in sleeper and partition walls.
Technically you should pipe duct the ventilation through the solid floor.

 

[Jud234]

Thanks. Daft question but can you ventilate into the extension as the base is lower than house floor ?

 

[Static]

You cant ventilate into a habitable area. The ventilation is mainly for gases and condensation.. you dont want that discharging into any room!

 

[Jud234]

What depth does the pipe need to be ?

 

[Static]

Urm little bit late isnt it to be thinking about that. What did the building control guy ask for exactly?

 

[Jud234]

He wants three vents piping into the existing house. Is the only way to cut into the concrete base.

Yes it is very late which is why it is very frustrating when plans have been approved without it being mentioned and two previous inspections carried out without it being mentioned, and thats not to mention the builder.

 

[Static]

To be honest is a mistake by your architect really, something they should have considered when doing the plans. Anyways.. to be honest ive never had to post fix ventilation like that and personally would have made the new extension a suspended slab so the old could be easily vented through. Sorry..
What kind of cover do you have to the concrete, what insulation and what screed?

 

[Jud234]

We haven't screeded yet, not sure about the insulation.

Is carrying out this work possible or is it going to create more problems ?

 

[Static]

Anything is possible if you have the money.. but lets assume you dont.
Simplest solution would be to run the vent through the upper concrete cover/insultation/screed layer if you have the room. Alternatively you may need to look at breaking out the slab locally to when the vents need to be.