Cold roof with no ventilation can it be done with Cromar Vent 3 Air

[actionjackson]

How do I convince my building contractor and build control we don't need eaves ventilation and can then benefit from improved thermal performance by removing wind washing of the insulation, reducing convection and possibly a better environment in the attic for MVHR systems?

 

We have a mix of existing and new conventional cold roof constructions with 400mm build up of mineral wool insulation that will soon be ready for "felt & batten". 

 

I have specified Pro Clima Intello as the vapour control layer which will be installed under the trusses behind the plasterboard ceilings and lapped onto walls.  Unfortunately, we don't have ceiling height to add a service void for lights and cables so we will have to be super diligent with sealing penetrations etc

 

The original building has 50mm cavity walls which will be pumped with insulation and 90mm of EWI (the new extensions have 150mm cavity and no EWI) - I await the final detail drawing from our consultant but believe 50mm of PIR will be installed at the eaves to improve insulation in a weak area plus "provide the required 25mm air gap" for eaves ventilation.

 

So much conflicting content on the cold roof ventilation debate so looking for others to share there experiences and insight.

 

Is Cromer Vent 3 air the answer or am I missing something?

[JohnMo]

Choose a product specifically with certification for what you want. Kingspan Nilvent comes to mind, but plenty of other available.

 

Look at the certificates and approvals.

 

Doesn't 

36 minutes ago, actionjackson said:

Pro Clima Intello

Allow two way humidity movement as it's a smart membrane? If so not sure you want unventilated roof space, but with correct roof membrane you still get plenty of air movement as they are vapour closed and air permeable. 

 

Get you ducks in row and the BBA certificates, then you should have no issues 

[ETC]

Read the BBA/BRE certificates. They will tell you if you need ventilation-some do and some don’t.

[JohnMo]

40 minutes ago, JohnMo said:

correct roof membrane you still get plenty of air movement as they are vapour closed and air permeable

Wrote that incorrectly. They allow vapour out, but air in and out and keep water out should you have issues with your tiles or slates 

[saveasteading]

57 minutes ago, JohnMo said:

Kingspan Nilvent comes to mind, but plenty of other available.

 

Look at the certificates and approvals.

Not that I trust Kingspan certificates.

[actionjackson]

Cromer Vent 3 Air is BBA certified for unventilated cold roofs and is good value so should tick the box.

 

Do we need to re-think the use of intello on our upstairs ceilings? 

[JohnMo]

2 minutes ago, actionjackson said:

Do we need to re-think the use of intello on our upstairs ceilings? 

Get manufacturer and industry (BBA/BRE) test certs and see what it is approved for.

[Gus Potter]

9 hours ago, actionjackson said:

We have a mix of existing and new conventional cold roof constructions with 400mm build up of mineral wool insulation that will soon be ready for "felt & batten". 

Lets see some drawings and details. Plan views and cross sections.

 

I do this as a day job and can tell you it is much harder than you think. 

 

Forget the BBA stuff, material selection at this stage and concentrate on the basics first. 

 

First step is to understand how your new stuff fits into the old. Then design something that your builder can build without pulling your pants down cost wise. You don't really know the setting out of your existing roof and wall head detail.. have you surveyed this critical bit yet? 

 

At the end of the day the objective is to produce some drawings that your builder and you think.. how simple and chep is that. But to get there you and your designer are going to have to put in a fair bit of work.

 

If you post the drawings you have then folk like me may chip in with some suggestions.