Why is outer leaf of blockwork left lower in rising walls?

[New build new]

Hi all,

 

I'm a novice builder, except for labouring jobs during the summer when in college. I'm now looking at building a home office at the back of my garden. I plan on doing this myself.

Originally I planned on building the rising walls in solid blocks on flat and the main structure in cavity blocks. From looking around it seems as if cavity walls are the preferred and better form of blockwork for construction i.e 100mm wall - 100mm cavity - 100mm wall.

 

The problem I have now is how to construct the rising walls for this type of construction? Any pictures I've found seems to leave the outer leaf of the wall down by a half a block or even a full block. Could someone explain why this is to me?? 

 

 

 

Thanks.

 

 

 

[Moonshine]

2 minutes ago, New build new said:

 

I'm a novice builder, except for labouring jobs during the summer when in college. I'm now looking at building a home office at the back of my garden. I plan on doing this myself.

Originally I planned on building the rising walls in solid blocks on flat and the main structure in cavity blocks. From looking around it seems as if cavity walls are the preferred and better form of blockwork for construction i.e 100mm wall - 100mm cavity - 100mm wall.

 

The problem I have now is how to construct the rising walls for this type of construction? Any pictures I've found seems to leave the outer leaf of the wall down by a half a block or even a full block. Could someone explain why this is to me?? 

 

You could go timber frame, a masonry cavity wall seems overkill for a home office.

 

I have never seen the outer leaf down half a block nor can figure out why it would be, given you couldn't fit wall ties in.

[keith65]

so you can do a stepped cavity tray

[Dave Jones]

not at dpc level.

[Brickie]

The  pictures you’ve posted are of footings. The outer leaf will have face brickwork up to dpc. 

[New build new]

19 hours ago, Dave Jones said:

not at dpc level.

 

Cheers for the reply Dave. On further investigation the inner leaf is at finished floor level. As Keith said, it seems to be for the introduction of a stepped cavity tray.

 

 

On 16/04/2021 at 07:32, keith65 said:

so you can do a stepped cavity tray

 

Yes I think so Keith. Would this be common practice or would it be on the drawing detail?

 

 

19 hours ago, Brickie said:

The  pictures you’ve posted are of footings. The outer leaf will have face brickwork up to dpc. 

 

Hi Brickie, thanks for reply. Yes I know these are footings. It appears that Keith is correct. The inner course is at ffl. The dpm will lap over and down onto the block on flat creating a tray. Then the outer leaf will be built up.

 

thank u all.

[Declan52]

The inner course is not FFL. On top of the ground in each of them pics you will have if possible hardcore then Dpm then insulation and a concrete sub floor or the finshed slab if that's how your doing the build.

FFL could be anywhere between 150-225mm higher depending on ground conditions and the amount of insulation your putting in the floor.

It's not for stepped cavity tray either. You can at this stage put one in but you only do a cavity tray like that if the outside ground heights are going to be higher than normal. It's left at this height so your first layer of cavity insulation boards/batts will be below the finshed floor level so no cold spot as your wall ties will start on top of the inner block work. This will leave a 225mm gap underneath where any motar droppings can fall to and not cause any issue.

The lower section is where you start the brickwork or blocks but both have to match height wise going up for the wall ties.

 

[Dex44]

To prevent any concrete spilling into the cavity when the subfloors are being poured. If your cavity was filled then any motar droppings would quickly rise above FFL allowing dampness in.