Our house has a flat roof construction with the following build up-

 

Open web joists

Airtightness membrane

18mm OSB deck

Vapour control layer

Tapered PIR insulation 150-350mm thick

Single ply fleecebacked EPDM membrane

 

The airtightness membrane used is a mixture of Siga and Ampatex DB90. The Ampatex membrane has been installed with the smooth printed side facing the OSB deck and the rough side facing into the house. Ampatex DB90 data sheet instructions indicate that the membrane should be installed with the smooth printed side facing into the house.

 

Does anyone have an opinion on whether this is correctly done? By the strict letter of the installation 

 

The smooth side is the only side that tape will adhere to, which is why the MIs say to install it smooth side in.  How are they taping the joints in the membrane?  Airtightness tape probably won't adhere well to the rough side.

Edited March 16, 20179 yr by JSHarris
typo, "is" when I meant "it"

The joints have been taped on the smooth side so there is no issue with the taping. Its just a question of whether the right side is facing into the room and right now I think its not.

 

http://www.ampack.eu/fileadmin/user_upload/ampack/00_Produktdaten/Bahnen/Ampatex_DB90/Datenblaetter/Data_sheet_Ampatex_DB90_lr_EU.pdf

Edited March 16, 20179 yr by ryder72

Reading the data sheet I'd agree with you, it does state clearly that it has to be fitted smooth side facing in.  I do not like the idea of having tape on the outside face of the membrane at all, that may well be against the tape manufacturers instructions, too.

 

With the rough side inwards, taping around any penetrations going through the membrane later will be impossible.

Edited March 16, 20179 yr by JSHarris

Jeremy thats a very good point I hadnt thought of. 

 

I dont know why they have done it how they have done it but it clearly looks like a problem.

 

Do you know what the moisture and air transmission properties of this membrane are?

Edited March 16, 20179 yr by ryder72

I'm afraid I don't.  We don't have a VC membrane in our build, it uses a vapour permeable board internally as the VCL.  There doesn't seem to be any info from Ampack on the detailed performance of this membrane that I've been able to find quickly.

I couldnt either. I suspect the membrane is air tight both ways but vapour permeable one way and I suspect that would be smooth side to rough side to allow moisture to trickle out but on in when installed smooth side in.

Further update-  Ampatex distributors have confirmed the the installation is correct in the context of the type of roof build up. The issue of sealing tape will be addressed with a liquid applied system they offer.

 

Thanks for your help Jeremy.

 

Glad to hear there's a simple solution to getting the tape to adhere, and that there's no need to undo the work that's already been done.