PIR Board Installation in Pitched Roof Loft - Concerns Over Installation

[A_Wonderer]

Hello, I'm new to DIYnot so I'll be interested to see what some of the more experienced tradesmen have to say here.

I've recently had 50mm PIR installed in my cold pitched roof, but I'm concerned about the install. Every manufacturers installation guidelines and tutorial video state there should be no gaps with a seamless build from eaves to eaves. But you can see from the images there has been large gaps left at the bottom edge - where I believe it should be in contact with the eaves (obviously without blocking airflow). I'm concerned this will create thermal bridging and condensate behind the PIR.

For context, this is just a workspace that won't be lived in for extended periods of time. But I want to make sure there are no future issues with condensation or mould. I'm also planning to fit a 500 gauge VCL. What I want to know is, am I over reacting? Will this cause us no issues? Bearing in mind, I've got 70mm soffit vents all along both soffits and will have 3 tile vents installed on both sides of the roof. Your feedback and guidance would be greatly appreciated. Thanks.

 

[Wayners]

It's the bottom that's the problem as the gap narrows.
You need to keep a 50mm space from the insulation to felt.
You will need a wall around the edge I guess to block the gap with insulation.
Then with vented soffit and vents in the roof near the top the air will blow through.
I used therma quilt with my loft conversion so that bent around at the bottom.

 

[A_Wonderer]

I've made sure there's a 50mm air gap between the PIR and felt, it's more the large gaps between the bottom edge of the PIR and the eaves walls - installation technique states you should have a continuous seem free installation, which this is not. Am I over reacting, or will this create issues in the future, and will the thermal performance drastically under perform.

 

[Wayners]

You are trying to make it air tight.
Any could air blowing in could cause condensation inside when it hits the warm moist air

 

[A_Wonderer]

Yeah, and by aiming for air tightness, the empty sections between the bottom of the PIR and eaves walls would not give air tight performance. However, when I questioned the guy about it he said the empty sections would improve airflow and circulation around the loft.. which in part is true.. but it also invites any warm air getting behind the PIR and causing condensation when it hits the cold felt.

I guess the bottom line is, am I over reacting? Will this cause no major issues, or should the empty sections at the bottom of the PIR be sealed and aluminium taped?

 

[cdbe]

I think you'd have been better with a dwarf wall and keeping the eaves clear, and a small flat ceiling in the apex to maintain good airflow - the standard way it's done in a loft conversion.

 

[A_Wonderer]

Yeah, to say I'm unhappy with what this guy has done is an understatement.

 

[freddiemercurystwin]

It is difficult to get down that part of the loft, otherwise he should build a vertical wall down there and insulate in that, to maintain the 'insulation bubble', there should be no air gaps, it might be possible to fill the gaps between the boards and rafters with foam where they're excessive, he could also tape over any joints with foil tape. But you will have a VCL, presumably you're boarding it afterwards? BTW unless you have continuous ridge vents then really you need a tile vent near the ridge between each rafter and on all pitches.

 

[A_Wonderer]

@freddiemercurystwin it's a tough one, because this isn't your standard "loft conversion" it doesn't need to look pretty, it's only a temporary work space - no one will be there for extended periods of time. His exact words on why he didn't tape below the trusses "it's a waste of time if you're putting a VCL over it"... Which is B.S if you ask me. I'm an engineer and understand how thermodynamics work, even with the VCL all timbers should be taped.

I won't be fully plaster boarding it, only the top half of the trusses along the length of the roof. I agree, those areas of the eaves are very difficult to reach. So the most viable option is the dwarf wall to maintain the insulation continuity.

Thanks for the advice everyone, I really appreciate it. I guess the penultimate question is, is this job acceptable enough for full payment of the work.. considering the extra work that'll need to go into it and the issues it could cause - especially during the colder months.