MVHR Ducting

[ZacP]

Hello all,

 

Just thinking about our build and how we’d best to install the MVHR. I’ll be doing this myself to bc save costs so trying to get as much knowledge as possible! 
 

I get running the ducts in voids in walls/floors however...

 

We are building in ICF, virtually all of the walls are going to be load bearing and therefore in more ICF or block and planning on a beam and block floor. Therefore no voids. Hmmm. I might run into difficulty with electrics and plumbing too, but seeing as the MVHR pipes are biggest then if that problem is solved the others should be easy!! 
 

MVHR likely to be in loft so top floor will be easy. Getting to lower floor is the challenge!

 

Thanks! 

[CC45]

down through cupboards etc into floor / ceiling voids. 

[ZacP]

@CC45 But we are having a insulated slab (no voids I hope!) and a beam and block first floor. My understanding if that these don't have voids?

[ultramods]

As @CC45 has said easier in an internal partition such as behind a cupboard or a void in bathroom/ensuite. If the first floor is going to be beam and block you will need to design in holes to allow the ducts to pass.

[Nickfromwales]

You can switch to rectangular ‘D’-shaped ducting to reduce the profile, and then make the service void under the 1st floor B&B a bit bigger to accommodate it. Run the ducts from the rooms back to the plant and then assign which duct does what, to make things easier on logistics as you won’t be able to have any crossovers if space-constrained. 
M&E design / foresight is critical in a B&B dwellings, so if that’s not been applied at a very early stage you may end up doing series vs radial eg if you are seriously struggling to get from attic > ground floor. 

[ultramods]

when I was considering ICF a few years ago I remember reading about large pre fabricated  concrete floor panels/cassettes that had ducts build in (added before the concrete pour). I'm not sure how expensive or practical there are.

[Nickfromwales]

  On 25/09/2020 at 08:43, ultramods said:

when I was considering ICF a few years ago I remember reading about large pre fabricated  concrete floor panels/cassettes that had ducts build in (added before the concrete pour). I'm not sure how expensive or practical there are.

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You’d still need to be able to get small bore services around too, so a service void is inevitable. The design logistics in the pre-ducted  / pre-serviced slabs would be off the chart. And if you’ve got it wrong you’re Donald Ducked. 

[ultramods]

  On 25/09/2020 at 09:04, Nickfromwales said:

You’d still need to be able to get small bore services around too, so a service void is inevitable. The design logistics in the pre-ducted  / pre-serviced slabs would be off the chart. And if you’ve got it wrong you’re Donald Ducked. 

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That's what I suspected

[ZacP]

Think I may change the design to pozi joists...

[joe90]

  On 25/09/2020 at 09:14, ZacP said:

Think I may change the design to pozi joists...

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Why did you want beam and block first floor?. I went with I joists (osb webs) quite easy to drill even for MVHR pipes, pozi joists even easier. BUT the only thing I would change with my build is to double board ceilings and resilient bars as the sound transference between floors is greater that I expected even with sound insulation fitted.

[markc]

  On 25/09/2020 at 08:43, ultramods said:

when I was considering ICF a few years ago I remember reading about large pre fabricated  concrete floor panels/cassettes that had ducts build in (added before the concrete pour). I'm not sure how expensive or practical there are.

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Having put up loads of commercial buildings with PCCP`s (pre cast concrete panels), the cast in ducts have always been a nightmare. Either colapsed during the pour/curing, didnt align with the next panel etc. or trying to break into a duct for a box opening etc. has been known to crack the panel.

[ZacP]

  On 25/09/2020 at 09:34, joe90 said:

Why did you want beam and block first floor?. I went with I joists (osb webs) quite easy to drill even for MVHR pipes, pozi joists even easier. BUT the only thing I would change with my build is to double board ceilings and resilient bars as the sound transference between floors is greater that I expected even with sound insulation fitted.

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We wanted it to feel solid and not echo as you walked on it. Also the sound transfer between floors (upside down house with kitchen living dinning above bedrooms) is relatively important, but if I beams and pozi joists can achieve this then I'm all for it

[joe90]

  On 25/09/2020 at 09:43, ZacP said:

 

We wanted it to feel solid and not echo as you walked on it. Also the sound transfer between floors (upside down house with kitchen living dinning above bedrooms) is relatively important, but if I beams and pozi joists can achieve this then I'm all for it

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fair comment about sound but is it worth the cost/hassle. Our builder specced joists at 600mm but installed at 400 to avoid bounce (which we have none) as I said above I wish I had double boarded and/or used resilient bars. Also attention to detail around the floor/ceiling can make a difference. Also just read somewhere about sound block flooring (additional boards with foam/rubber membrane fitted to floor to block sound).

[Nickfromwales]

  On 25/09/2020 at 09:14, ZacP said:

Think I may change the design to pozi joists...

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Get them at 400mm centres apart MAXIMUM.  
There is very obvious bounce ( aka deflection ) at 600mm c’s. Asking for an extra run of strong-back won’t go amiss either and is pennies in cost terms. 

[Nickfromwales]

  On 25/09/2020 at 09:58, joe90 said:

fair comment about sound but is it worth the cost/hassle. Our builder specced joists at 600mm but installed at 400 to avoid bounce (which we have none) as I said above I wish I had double boarded and/or used resilient bars. Also attention to detail around the floor/ceiling can make a difference. Also just read somewhere about sound block flooring (additional boards with foam/rubber membrane fitted to floor to block sound).

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https://www.rubberco.co.uk/selectedsize/sound-proofing-and-deadening-rubber-sheet-linear-meter/4103?gclid=Cj0KCQjwqrb7BRDlARIsACwGad7BaSmHXn3AA732nmgLKChgqw2yeRS1uwnXpcLV6lmTTU8fJwVzGA0aAp0vEALw_wcB
 

This stuff takes a lot of the foot traffic / other impact sounds down a good few notches. Deffo go for acoustic batt and double up on acoustic boards or resilient bars and one layer of 15mm acoustic board. As said, dealing with the detail at the perimeter is often overlooked. Stuff some loose rock wool in there to plug everything up nicely. 

[dpmiller]

poured screed on pozijoists is pretty firm.

[joe90]

  On 25/09/2020 at 10:38, dpmiller said:

poured screed on pozijoists is pretty firm.

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@ZacP are you having UFH upstairs? You could do like @ProDave and put pipes in a biscuit mix which would deaden a lot of sound  !

[ZacP]

@joe90 I like biscuits but can’t see how they’d help with sound deadening. Except when I’m eating them I’m generally not walking around! 
 

yes to UFH. Wold this go between the joists or in screed above as mentioned by @dpmiller? 

[joe90]

  On 25/09/2020 at 11:23, ZacP said:

Wold this go between the joists or in screed above as mentioned by @dpmiller?

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Can be either, see.   http://www.radicalheatingsolutions.co.uk/underfloor-heating/joisted-floor/biscuit-mix/   As an example. They talk about extra thermal mass (incoming....?...) this will add to sound absorbency . Your floor must be designed to take the extra weight tho!.

[ZacP]

Ok, I’ll look into that, thanks @joe90! 
 

what’s the deal with thermal mass? Guess it’s a marmite situation?

[joe90]

The Great Thermal Mass Myth.......

 

read this thread,  bit of an in joke on this forum

 

(how do you post a thread, can’t find it on my iPad)!

Edited September 25, 2020 by joe90

[CC45]

  On 25/09/2020 at 10:08, Nickfromwales said:

Get them at 400mm centres apart MAXIMUM.  
There is very obvious bounce ( aka deflection ) at 600mm c’s. Asking for an extra run of strong-back won’t go amiss either and is pennies in cost terms. 

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This is VERY GOOD advice.  Ours are at 600mm - OK but way better with 400mm.  Use the pozi joists 600 spec with a 400mm gap.  You should be fine with that.