Anyone mounted a Ubbink UB48 MVHR vent from above?

[Alan Ambrose]

… and made it an airtight seal with the roof. This guy:

 

https://www.ubbink.com/gb/products/building/roof-terminals/pitched-roof-terminals/roof-terminal-insulated-ub48-180mm-black/

 

Best idea we have is to cut the pipe, install in the roof, and then use a SC200 rubber pipe connector to join the stuff above - assuming we can get to it.

[MikeSharp01]

Nope but I am going to - in the near future. So I can perhaps share the journey. Let's hope we can get advice. 

 

In our case we don't yet have the slates on so that I am hopeful that will simplify things.

 

[JohnMo]

Why don't you use ubbink foam duct? Ubbink website states

 

Designed to fit Aerfoam 160 mm & 200 mm, with adaptors available for 150 mm and 180 mm

[Nickfromwales]

3 hours ago, Alan Ambrose said:

… and made it an airtight seal with the roof

Eh? You mean weathertight? 

[Alan Ambrose]

>>> Why don't you use ubbink foam duct?

 

I am, this drops into 180mm foam duct.

 

>>> You mean weathertight? 

 

I am mainly concerned about the airtightness of the ply box that is the roof (that has the foam duct running within) - there’s a membrane and a metal roof to go on top.

 

The main problem is logistical - I’ll take a few pics when I’m up there. Ubbink (who are not good designers imo and have clearly never installed their own products in anger) seem to assume the whole contraption pokes through into an attic where it can be joined to the duct afterwards. (Although how it would be sealed, I can’t imagine.) I have the duct in place and a hole in the right place in the ply and want to install from above. Unlike some Ubbink roof terminals, this one doesn’t seem to be designed to be installed sequentially from above. If the cowling could be installed last following the 2nd sleeve that would work. But that’s not how it’s designed.

[JohnMo]

3 minutes ago, Alan Ambrose said:

am, this drops into 180mm foam duct

Use ubbink joints then.

 

5 minutes ago, Alan Ambrose said:

mainly concerned about the airtightness of the ply box that is the roof (that has the foam duct running within)

Suspect the terminal is designed to go through roof from a cold loft that is outside the airtight envelope. If your doing some different you may have chosen the wrong product.

[Alan Ambrose]

>>> you may have chosen the wrong product.

 

Possibly, I think that’s the only Ubbink choice for the flow I need. But … I’ve found elsewhere that the Ubbink range doesn’t appear to have had a lot of thought behind it. Will see if I can cobble together a hack.

[Gus Potter]

On 20/03/2026 at 17:11, Alan Ambrose said:

and made it an airtight seal with the roof.

If you have corrugated steel profile roof sheeting something like this may be more suitable for the weathering detail.

 

 

Your air tight layer is further into the depth of the roof. The issue is sequencing of the build process. Weather proof steel sheeting is probably going to go on first before you start to introduce plasterboard and air tight layers. You probably need a second flashing to pipe gizmo that you can bond to your air tight layer. 

 

Your air tight layer is usually a plastic membrane so we need something that you can use to bond the plastic to the soil pipe. Remember that soil pipes expand and contract a bit when you empty the bath warm water for example, thus we need something flexible. Can we just rely on air tape or do you want something more " professional" looking.  Like this:

 

 

 

 

 

 

 

 

 

[Alan Ambrose]

Gus, you are a mine of information as usual. Maybe we can have you cloned by AI at some point .

 

I didn't think to ignore the flashing that came with the vent and use a different flashing. Genius. Will report back.

[Nickfromwales]

On 21/03/2026 at 09:28, Alan Ambrose said:

If the cowling could be installed last following the 2nd sleeve that would work. But that’s not how it’s designed.

The sequence for installing the Ubbink ones is correct, as the rain falls down the outer edge it steps out (where the final part hits the make part of the flashing) to give a robust weathertight seal.

 

 

 

This job is an MBC PH TF with 400mm roof void. I just extended the foam ducting before installing these, then made everything off inside the attic plant room below. 
 

Im not sure what your exact issue is, as I don’t assume you’ll need the MVHR running before your roof is finished? 
 

You just lift the terminal out of the flashing and then install it, and if you need weathertight for a few weeks or months (or years ) you just drop the terminal back in and mechanically fix it in place. 

[Alan Ambrose]

>>> 400mm roof void .... then made everything off inside the attic plant room below.  Im not sure what your exact issue is

 

@Nickfromwales

 

Yes, you can install by putting in the terminal from above and then completing the install from below.

 

But .... you can't do the reverse.

 

Imagine you have the foam pipe already installed in your warm roof. You want to install the vent pipe, then slip over the two flashing pieces at a later date. You can't (as designed) as the cowl (and the little welded on lip) is fixed on the pipe and the flashing won't slip over it. This is unlike, say, the Ubbink UB41 terminal where you can install the flashings from above. You can't tell from the images or the install instruction's (for either the UB41 or 48) that that's the case until you have the product in your hands.

 

The design solution would have been to make the cowl and the welded on lip halfway down the pipe detachable to allow this.

 

And ... there are no dimensional drawings on the Ubbink site, which marks them out as amateurs imo.

 

Edited March 23 by Alan Ambrose

[Nickfromwales]

30 minutes ago, Alan Ambrose said:

>>> 400mm roof void .... then made everything off inside the attic plant room below.  Im not sure what your exact issue is

 

@Nickfromwales

 

Yes, you can install by putting in the terminal from above and then completing the install from below.

 

But .... you can't do the reverse.

 

Imagine you have the foam pipe already installed in your warm roof. You want to install the vent pipe, then slip over the two flashing pieces at a later date. You can't (as designed) as the cowl (and the little welded on lip) is fixed on the pipe and the flashing won't slip over it. This is unlike, say, the Ubbink UB41 terminal where you can install the flashings from above. You can't tell from the images or the install instruction's (for either the UB41 or 48) that that's the case until you have the product in your hands.

 

The design solution would have been to make the cowl and the welded on lip halfway down the pipe detachable to allow this.

 

And ... there are no dimensional drawings on the Ubbink site, which marks them out as amateurs imo.

 

I think some rather messed up sequencing is afoot here tbh. I've never had a single issue and have used Ubbink for as long as I can remember. Only time I abandoned them was for a very steep roof on a project near Melton Mowbray where Nick from CVC got me some bespoke lead cowls made up to fit into the Ubbink downfacing 'female' bit. Worked a charm.

 

Not a pork pie in sight  

 

Norm for us is to install the flashing and terminal with the roofers, then once weathertight the MVHR unit goes in, and we hook up?

[Alan Ambrose]

OK, for anyone else with the same problem, we:

 

+ drilled holes in the cowl so we could easily access the screws holding it on - and then removed the cowl.

+ cut the pipe to the right finished length. That’ll mean padding the cowl fixings a few mm as the pipe flares a bit at the top. We could have instead cut the lip off that sits above the highest flashing.

+ junked the two flashings and the remaining bit of pipe.

 

To install from above we’ll:

 

+ insert into the foam pipe below with an extra bit of mastic for good luck. (Actually into the thin 180-200mm adaptor that we’ve installed into the end of the foam pipe.)

+ mastic the exit through the ply skin for first level of airtightness. Then tape then use the bottom gasket that Gus suggested.

+ strap with the strap supplied for support. We may add an extra strap and also thin EPDM strip to prevent squeaking with thermal expansion.

+ add our metal roof and then the 2nd gasket that Gus suggested.

+ screw on the cowl.

Edited 10 hours ago by Alan Ambrose

[Gus Potter]

9 hours ago, Alan Ambrose said:

OK, for anyone else with the same problem, we:

Post a photo of where you are are the moment.