Under Floor Vents for Block and Beam through ICF

[Dean Mc]

Hi all,

 

We are building our home from Nudura XR35 on a sloping site and have only stacked and poured up to floor level so far, ready to take our block and beam flooring. It's only just been noticed that there should have been some underfloor ventilation fitted for the cavernous void underneath, as per the approved architects drawings. They've advised a vent every 2m each side of a 12m run. The site is on the side of a hill, very exposed and regularly subjected to >50 MPH winds. 

 

We were supposed to fit something along the lines of the Manthrope telescopic underfloor vent, but I'm aware they are pretty flimsy and prone to shattering / cracking under the pressure of the next pour:

https://www.screwfix.com/p/telescopic-underfloor-vent-black-220mm-x-215mm/12025

 

An option I have is to drill 4" / 100mm holes through the Nudura and concrete and fit a vent / tube / grill assembly. 

 

I maybe over thinking things, but one of my worries is wind whistling through the vents even if make a swan neck? Likewise, making something too truncated and it not providing sufficient ventilation.

 

Anyone had similar experiences or had to address anything similar? 

 

[Russell griffiths]

Talk to building control. 

I have ventilated all mine, but a friend down the road said bc told him it was pointless, if he didn’t have ground gasses to ventilate out then vents were not needed. 

 

How will you drill through and get the vent to be below floor level but above ground level. 

 

whos Fault was it they were missed off, I would not be  impressed. 

[Dean Mc]

I was hoping to get the floor in this weekend, so would / will have to wait to speak to BC.

 

We're building on a hill, so the topography of the ground slopes away. We've had to build up above ground over 1m to get to floor level so the ICF is still exposed. 

[Russell griffiths]

So if you are above ground level you can just core hole through, you will need to calculate the square mm of a 100mm vent and compare it to an airbrick, you might need to add extra. 

 

As for the wind noise, you won’t hear that in the house, you will have a dpm lapped against the inside Nudura and taped on, then your insulation which should be a good fit and even foamed at the edges, then a further thin plastic, then screed, which when dry can be sealed against the Nudura. 

Not a whisper getting through that lot. 

This is what I did and part of the method to getting a good airtest result. 

[Dean Mc]

Awesome, thanks for that @Russell griffiths 👍

[saveasteading]

I like there always to be ventilation in a floor void. If dampness can get in somewhere, anywhere, then it should be allowed out again.

In your case on a slope there is also a strong chance of water getting in, so I suggest holes at ground level on the downhill side...covered against insects.

[Dean Mc]

6 hours ago, saveasteading said:

I like there always to be ventilation in a floor void. If dampness can get in somewhere, anywhere, then it should be allowed out again.

In your case on a slope there is also a strong chance of water getting in, so I suggest holes at ground level on the downhill side...covered against insects.

TY. That's just raised a few more Qs in my head now 🤯😆

[ChrisJ]

Too late for you now, but the off cuts from your block, you can cut and insert into the top of the vent to prevent crushing during the placement of concrete

[Dean Mc]

Thanks ChrisJ,

I kind of dismissed that at the beginning, as I thought it may crush? I was thinking along the lines of.... I appreciate the Nudura takes the outward forces but has the internal ties increasing strength and preventing distortion. Does it resist 3m worth of concrete being poured on top?

 

I've been thinking of far more complicated, time consuming and costly solutions including manufacturing stainless shrouding and ducts and all sorts. Although I had thought of inserting timber inside the duct, but didn't know how easy it would be to remove and I'd possibly end up with blocked Manrose vents and still having to core drill extra holes too 😬