How to drill holes through my external wall for the big MVHR ducts?

[Dreadnaught]

How do I go about drilling holes in my exterior walls for MVHR ducts (2x) to atmosphere? 

What tools should I use? How should I do it? Guidance, suggestions & tips most welcome!

 

External walls (closed cassettes)

 

• OSB, 12.5mm, Smartply Propassiv – inside
• Empty cavity 240mm, to be later filled with blown-cellulose insulation. Studs every 600mm.
• Magply, 9mm – outside
• House warp: Tyvek Firecurb

 

Ducts (2x)

 

• Ubbink 160mm (internal diameter) insulated ductwork
• External diameter: 192mm
• 

 

External cladding (not yet installed): Cedral lap planks (190mm, 30mm overlap), over treated battens.

 

External wall terminals (x2):

 

 

 

[markc]

Hole saw (short reach so needs pilot hole or guide sleeve, or Diamond core drill, will cut through masonry , steel and wood etc,  and maintain hole diameter and straight.

Edited November 18, 2021 by markc

[Nickfromwales]

Jigsaw on internal, and guess what you’d use externally? ???

 

 

Yup. The same jigsaw. A few minutes work each hole. A 200mm hole saw will be cumbersome and single use. The jigsaw will become a friend through your build, alongside his best mate; the multi tool. ?

[Mr Punter]

Wit a long bit, drill a hole straight through sloping slightly down from inside to outside and mark your outline both sides with pencil and string.  You might find it easier to clad right over with the Cedral and cut it with your cordless jigsaw.  I have used some Bosch fibre blades for cement cladding.  They cut really well and don't burn out.

[saveasteading]

If it was 150 or less then I would use a hole saw. It is easy and a clean and precise cut.

But they don't seen to exist above 160, so jigsaw seems to be the way.

[markc]

https://www.darttoolgroup.com/holesaws/dart-200mm-holesaw-dah200

i use them regularly, dart are on par with Starrett.

[saveasteading]

2 hours ago, markc said:

dart are on par with Starrett.

Good to know. I couldn't see 200 on Starrett. The reviews are good which explains why this is £50.

But for 2 holes, perhaps not .... jigsaw.

[Dreadnaught]

Good suggestions. Thanks all!

 

One problem.

 

For the inside holes I will be cutting through the span of a posi-joist, which is positioned against the wall. 

I don't think there will be enough space for a jigsaw.

The posi-joist is 304mmm, so a 200mm howl will only just fit, as follows:

[saveasteading]

yours is 192mm so looks ok but very precise work in lining up your wall hole.

How precisely are the joists laid? a few mm +/-  may give you issues. 

 

Is there any concern that your pipe could vibrate and transfer noise to the joists and then room?

[Dreadnaught]

Just now, saveasteading said:

How precisely are the joists laid? a few mm +/-  may give you issues. 

 

I checked them with a tape measure so all looks well.

 

Just now, saveasteading said:

Is there any concern that your pipe could vibrate and transfer noise to the joists and then room?

 

Good point. It is foam mass-flow ductwork so I think it should be OK. It should absorb any vibration. And, too, the joist in question only serves a utility room and the main bathroom, fortunately not a bedroom.

 

[Nickfromwales]

5 hours ago, Dreadnaught said:

One problem

How far from the inside edge of the pozi to the internal PP panel? Maybe a recip saw will be the weapon of choice if you cant get a jigsaw in there. I'd rather buy a tool I know I'll use again vs a one-shot tool that will gather dust from that day onwards.

Or,

https://www.screwfix.com/p/erbauer-adjustable-holesaw-with-cowl-29cm-9-piece-set/2571V?tc=FB3&ds_kid=92700055262507123&ds_rl=1244066&gclid=Cj0KCQiAkNiMBhCxARIsAIDDKNXkPP7NLdl4oP0CRkpnaiIufaNeLkbkj04xNZWniNY_IihSVsxYZwQaAlU7EALw_wcB&gclsrc=aw.ds

 

Can be used for cutting spots out etc later so multiple uses for that. The cowl on that will need to be removed to get in between the webs of the joist, and you'll need balls if steel for that.

 

Me personally, I'd just remove a 600mm square of the external board, cut the PP panel from outside in with a jigsaw / multitool / recip saw and refit. Drill a centred pilot through the hole you just made to mark the external panel, after glueing and screwing it back to the 600mm c'd vertical frame spines, and then cut out with the jigsaw..

[Gus Potter]

5 hours ago, saveasteading said:

yours is 192mm so looks ok but very precise work in lining up your wall hole.

How precisely are the joists laid? a few mm +/-  may give you issues. 

 

Is there any concern that your pipe could vibrate and transfer noise to the joists and then room?

Good spot.. learn something new here every day here!

[Dreadnaught]

9 minutes ago, Nickfromwales said:

How far from the inside edge of the pozi to the internal PP panel?

 

The pozijoist is touching the wall.

 

8 minutes ago, Nickfromwales said:

Me personally, I'd just remove a 600mm square of the external board, cut the PP panel from outside in with a jigsaw / multitool / recip saw and refit. Drill a centred pilot through the hole you just made to mark the external panel, after glueing and screwing it back to the 600mm c'd vertical frame spines, and then cut out with the jigsaw..

 

Ingenious!

 

Thank you to everyone once again for more ideas.  I'm back on site on Saturday and I will be up on my step ladder again for another look… and think. 

[Nickfromwales]

https://www.ukplanettools.co.uk/makita-djr185z-18v-mini-receiprocating-saw-bare-unit-djr185z.html?gclid=Cj0KCQiAkNiMBhCxARIsAIDDKNUTPeD7VSND-NSUnD2RhIRzVhBftiEKPOfDlxKp4XFol7P5rhfZ18MaAlrsEALw_wcB

 

[Dave Jones]

chainsaw for a shed construction!! 

 

easy!!!

[Dreadnaught]

I have a question about how high to drill the the holes.

 

Back on site, I had another careful look at the position of the holes. I realised that I cannot drill through the span of a posi-joist as I planned. This because I would be cutting through the top of the wall cassette, so hitting the horizontal I-beam that is its cap. This means that I will instead lower the holes beneath the ceiling of the plant room, which will make the drilling easier anyhow. (This in turn means that, to achieve my desired separation between intake and exhaust (of 1.5 m) that I will run the intake duct through the stud wall in to the neighbouring Utility Room.)

 

My new question: I have high ceilings, 2.8 m. Now that the holes are below the ceiling, how low can they go? Could be at 2 m height? Could they be even lower? Or is higher better?

[Dreadnaught]

By the way, I intend to put a in-line pre-filter box on the intake like this. This will be a coarse filter so as not to add too much resistance to the air flow. And which will catch errant flies and so on.

 

WIth the new duct runs, this could now be in the neighbouring Utility Room: more easily accessible for filter changes.

 

I am a bit cornered about condensation forming, on the inside in summer and outside in winter. I may look to have a tray underneath to catch any condensation.

 

[shuff27]

8 minutes ago, Dreadnaught said:

I have a question about how high to drill the the holes.

 

Back on site, I had another careful look at the position of the holes. I realised that I cannot drill through the span of a posi-joist as I planned. This because I would be cutting through the top of the wall cassette, so hitting the horizontal I-beam that is its cap. This means that I will instead lower the holes beneath the ceiling of the plant room, which will make the drilling easier anyhow. (This in turn means that, to achieve my desired separation between intake and exhaust (of 1.5 m) that I will run the intake duct through the stud wall in to the neighbouring Utility Room.)

 

My new question: I have high ceilings, 2.8 m. Now that the holes are below the ceiling, how low can they go? Could be at 2 m height? Could they be even lower? Or is higher better?

 

I'm at the design stage for MVHR.  My supplier is ADM Systems & their designer who is working on my layout says that low is no problem as long as they're high enough to avoid any external blockage, e'g. snow drift.  So mine will be at approx 1m above ground level.  The added benefit is shorter ductwork from the unit - internally they'll be concealed beneath the half landing of the staircase.

[Dreadnaught]

15 minutes ago, shuff27 said:

So mine will be at approx 1m above ground level. 

 

Ah thanks @shuff27, that's helpful to know.

[Gone West]

2 hours ago, Dreadnaught said:

My new question: I have high ceilings, 2.8 m. Now that the holes are below the ceiling, how low can they go? Could be at 2 m height? Could they be even lower? Or is higher better?

Ours were around 2.5m above outside ground level. We had to be able to brush insects off and wash them once a year.