External Cracks Between Original House & Single Story Extension

stuart45

It does both. If you butt a 13 inch wall against another wall, it won't fall along the wall, but in time can move away if not tied to the existing. We used to use frame cramps before starters came out. When a wall isn't tied, even a thick one it often moves away from the wall. 
But if you don't agree it's up to you.

grumbler

stuart45 said:

It does both. If you butt a 13 inch wall against another wall, it won't fall along the wall, but in time can move away if not tied to the existing.

Absolutely. And as soon as it moves away a fraction, it loses support - if not tied by the wall starter kit. With the kit if it moves away a little the support remains. This kit, basically, does the same job as slip ties, but the latter are impossible to use if one wall already exists.

stuart45

Slip ties allow for more movement as is needed on a movement joint. A wall starter or frame cramps still help with lateral and movement away from the wall

weeg

grumbler said:

stuart45 said:

It does both. If you butt a 13 inch wall against another wall, it won't fall along the wall, but in time can move away if not tied to the existing.

Absolutely. And as soon as it moves away a fraction, it loses support - if not tied by the wall starter kit. With the kit if it moves away a little the support remains. This kit, basically, does the same job as slip ties, but the latter are impossible to use if one wall already exists.

The new wall shouldn't need support from the existing in good design. (The old one might be designed to be supported from the new, if you've also removed existing supports/ knocked big holes in it. I'd always specify that the old and new founds are tied together if that's the case). Like a standard wall tie, you don't want any movement to occur between the old and new if you are using wall starters.

Slip ties on the other hand you use where you specifically do want the walls to be able to move relative to each other. Expansion and contraction due to weather.

Of course, you can use slip ties in a wall starter. I don't think I ever have, but I can imagine a scenario where you would (I'm thinking about piled blocks of flats, with an adjoining bin store, which is too lightweight to be worth piling, so designing for movement is prudent)

stuart45

grumbler said:

stuart45 said:

It does both. If you butt a 13 inch wall against another wall, it won't fall along the wall, but in time can move away if not tied to the existing.

This kit, basically, does the same job as slip ties, but the latter are impossible to use if one wall already exists.

Who told you that? I've use slip ties with wall starters on a block job which allowed for shrinkage in a long wall. They make them for the starter kit if required.

grumbler

weeg said:

grumbler said:

stuart45 said:

It does both. If you butt a 13 inch wall against another wall, it won't fall along the wall, but in time can move away if not tied to the existing.

Absolutely. And as soon as it moves away a fraction, it loses support - if not tied by the wall starter kit. With the kit if it moves away a little the support remains. This kit, basically, does the same job as slip ties, but the latter are impossible to use if one wall already exists.

The new wall shouldn't need support from the existing in good design.

How come? What's 'good design'?

Any highish brick wall has to be supported either by pillars or by other perpendicular walls. Gable walls have to be strapped to several rafters.  Of course, you can build a wall that thick, that it won't need any support. Is it what you call 'good design'?

Do you remember this recent thread - Putting a extra garage door in the rear wall of my garage ? Generally, I agree that if the back wall is removed, some extra support has to be provided to the side walls.

And, whatever you and your SE friends say, I stick to my guns. Wall starter kit is designed to stop the new wall from falling in the first place. It's too week for anything else.

(The old one might be designed to be supported from the new, if you've also removed existing supports/ knocked big holes in it. I'd always specify that the old and new founds are tied together if that's the case). Like a standard wall tie, you don't want any movement to occur between the old and new if you are using wall starters.

I want a lot of things. Unfortunately, what I want and what I can isn't the same. If the foundation is poor and starts subsiding, no ties are capable of holding the new wall.

Slip ties on the other hand you use where you specifically do want the walls to be able to move relative to each other. Expansion and contraction due to weather.

Again, I don't want walls to move, but I cannot prevent this. Hence, I make movement gaps to prevent cracks appearing as a result of the movements that I cannot prevent.

stuart45

When wall starters first came out BRE tested them and the resistance was about 4kn for a storey, depending on a good fixing. This is enough for normal movement in a building. Subsidence is different and a building will crack whatever you do. 
The main advantage of toothing is that the loads are spread more evenly through the wall, whereas with a starter there is a shear force at that point.

JKS$(

weeg said:

To actually answer the OP, it's a pretty poor design having the door hard against the original building. There's a few possible explanations, and anything anyone says here can't be more than speculation without seeing the building in real life. 
That's a uPVC door, and it's possible that some structural timbers were removed when it was installed. Or the lintel bearing isn't adequate. Or the founds are inadequate. Or the extension was never properly tied back. My guess would be it's an issue with the door opening, but it depends on the age and construction of the extension, as well as where in the country it is.

Thanks for all the replies - I'm not really following the technical aspects too well, but interested to hear everyone's' thoughts.

The house is on a hill in an area with historic mines in S. Wales. No idea about the type of soil but a 35 acre new housing development has planning permission within a few miles of the property. 
There is an internal crack in the middle wall of the original house -
 

Here's the rear view - does this help with discussion about foundation depth?

stuart45

You can't tell the foundation depth from the photo, but it looks to be quite a steep sloping site. It will probably a stepped strip foundation. It does make the end of the extension slightly heavier than the door end, which can cause differential settlement .
It's the opposite of how you build a buttress wall which drops off the weight as you go up, and it tends to settle towards the wall and keep the pressure against it.
It cracks do appear they are normally at the frames which are a weak spot in the wall.