Jump to content

Wall construction and airtightness around posi-joists


Recommended Posts

We're using 253mm high posi-joists (Mitek system already purchased) for our two storey detached house. The reason for using posi-joists is MVHR.

 

The posi-joists will sit on top of the 100mm blockwork inner skin at the required height (we are not using joist hangers).

 

We are planning to use the tony tray technique for airtightness around the joists.

 

The problem is the joists are 253mm high (compared to blocks which are 225mm high with the mortar joint), so am I correct in thinking we will need to notch out a bit of the block above around the top of each joist (to enable the blocks to continue up in sync with the external skin) and carefully lap the membrane around the notch as we go?

 

Thanks

 

 

Edited by Johnny Jekyll
Link to comment
Share on other sites

Who did the drawings or design and worked out the joists are 253mm high? Can you ask them (presuming they design and sign off on the calculations) if you use joist hangers as it  would make things far easier?

 

While possible it will be very messy and time consuming trying to have the membrane stretch around the notched ends of the blockwork. 

Link to comment
Share on other sites

29 minutes ago, Dudda said:

Who did the drawings or design and worked out the joists are 253mm high? Can you ask them (presuming they design and sign off on the calculations) if you use joist hangers as it  would make things far easier?

 

While possible it will be very messy and time consuming trying to have the membrane stretch around the notched ends of the blockwork. 

 

Thanks, unfortunately the posi joists are already on site so gotta find a way around it. Notching the blocks looks like it will have to be. 

Link to comment
Share on other sites

1 hour ago, Dudda said:

Who did the drawings or design and worked out the joists are 253mm high? Can you ask them (presuming they design and sign off on the calculations) if you use joist hangers as it  would make things far easier?

 

While possible it will be very messy and time consuming trying to have the membrane stretch around the notched ends of the blockwork. 

 

The joists were at 253mm so that the mid floor area would have enough room for both steels and MVHR ducts to run past each other. Very annoying I know.

 

Link to comment
Share on other sites

You can use joist end caps - only cost £4/5 each depending on size.  I have used them on mine and can grab some photos when back to site tomorrow if you want?

 

These allow for the timber shrinkage and have a foam airtight seal facing the block.

  • Like 1
Link to comment
Share on other sites

The joist lift is a pain in the arse for brickies either way and they will have priced for a fair amount of faffing about you would have thought.  To give you an idea the joist lift on mine was £3500 (labour) vs £5k for the 1/2/3rd lifts.

  • Like 1
Link to comment
Share on other sites

4 hours ago, Faz said:

You can use joist end caps - only cost £4/5 each depending on size.  I have used them on mine and can grab some photos when back to site tomorrow if you want?

 

These allow for the timber shrinkage and have a foam airtight seal facing the block.

Yes please photos and a website link if possible to where I can see them would be great. Thanks.

Link to comment
Share on other sites

1 hour ago, Faz said:

The joist lift is a pain in the arse for brickies either way and they will have priced for a fair amount of faffing about you would have thought.  To give you an idea the joist lift on mine was £3500 (labour) vs £5k for the 1/2/3rd lifts.

Again great info thanks.

Link to comment
Share on other sites

28 minutes ago, tonyshouse said:

I would ask about notching the top of the position joist or redesigning them to be 225 high where they go in the wall. Unlikely but theoretically possible 

 

love the idea of the tony tray ?

The joists are already here so another order would cost £1500+ 

I'll ask the bricky and see what they say. Thanks.

Link to comment
Share on other sites

20 hours ago, Johnny Jekyll said:

Yes please photos and a website link if possible to where I can see them would be great. Thanks.

Here you go mate.  As you can see from the box they came from Manthorpe - the merch will be able to source them for you.

 

The sudden summer makes life hard on site when it comes out of nowhere btw!

20210331_154649_resized.jpg

20210331_154612_resized.jpg

  • Thanks 2
Link to comment
Share on other sites

4 hours ago, Faz said:

Here you go mate.  As you can see from the box they came from Manthorpe - the merch will be able to source them for you.

 

The sudden summer makes life hard on site when it comes out of nowhere btw!

 

Thanks very much Faz.

 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...