Airtightness detailing - Timber frame to Masonry

[john0wingnut]

Hi all

 

My timber frame extension will be coming off of a masonry gable end and sitting over a brick / block foundation to DPC level.

 

Should one be using flexifoam / expanding foam tape behind the ledger board / under the soleplate / between first stud and masonry etc to ensure airtightness? 

 

I've also seen that one could use EPDM / Neoprene foam which can come in varying widths and thicknesses.

 

Might sound daft to ask, but if using a foam tape, should one apply 2 rows to the timber, so the timber is pulled in flat to the masonry / block? Eg if you put a foam tape only on the outside edge, it may angle the timber slightly when tightened in/down.

 

Or am I massively over thinking this?

[Roundtuit]

I'd foam any gaps between the dpm and frame to minimise cold bridging, but suspect you won't get much in, and that's not really an airtightness solution I don't think.  What's the airtightness strategy for the rest of the extension?  Membrane taped to masonry?

[Iceverge]

6 hours ago, john0wingnut said:

Hi all

 

My timber frame extension will be coming off of a masonry gable end and sitting over a brick / block foundation to DPC level.

 

Should one be using flexifoam / expanding foam tape behind the ledger board / under the soleplate / between first stud and masonry etc to ensure airtightness? 

 

I've also seen that one could use EPDM / Neoprene foam which can come in varying widths and thicknesses.

 

Might sound daft to ask, but if using a foam tape, should one apply 2 rows to the timber, so the timber is pulled in flat to the masonry / block? Eg if you put a foam tape only on the outside edge, it may angle the timber slightly when tightened in/down.

 

Or am I massively over thinking this?

 

Tape the membrane to the floor internally for airtightness and the breather membrane to the rising blockwork externally for windtightness.

 

 

[john0wingnut]

Internally I will be using SIGA Majrex 200, and the advice with that is to is use Fentrim tape or Primur tape to bond the membrane to the brick, and then use Sicrall tape on all the other corners / joins between membrane etc. This membrane will also be taped to the DPM.

 

Externally I will be using SIGA Majvest 700 Black UV membrane.  This will be taped to the roof deck before timber hard edge fitted, and I will also tape the deck joints with wigluv or fentrim tape

 

Re DPC junction, I had planned to leave excess DPC hanging out, then bring it up over the Steico Protect boards and tape external membrane to it. Not sure if that will work mind. The DPC is at the minimum 150mm above FGL, and cladding also finishes at this level on the detail, so if I taped down over that joint onto the bricks, I would end up seeing the tape as it would be lower than the cladding.

 

Re Masonry junctions:

Roof deck - was going to use expanding foam tape in this gap.

Walls - external membrane brought behind and around first batten, SIGA primur sealant put in gap, then pushed against masonry, and screwed in. Expanding foam tape could also be used here.

 

What I wasnt sure about is whether one needs to detail each element as you go, or just belt and braces internally / externally with membranes and all is well, so to speak

Edited May 14 by john0wingnut

[Roundtuit]

I'd foam and gap-fill as you build; any air movement through the structure is bypassing the insulation, but your membrane and tape will do the airtightness job.

[john0wingnut]

37 minutes ago, Roundtuit said:

I'd foam and gap-fill as you build; any air movement through the structure is bypassing the insulation, but your membrane and tape will do the airtightness job.

I might just buy a load of 15mm wide 1-7mm expanding foam tape and use as required then.