FOXFISH1 Registered User

What are the various acceptable methods of tying the new blockwork of the extension in with the exsisting blockwork of the exsisting dwelling.

Is it definitely necessary to dig into the exsisting blockwork (ie remove a block from every second row)?

Or is there another way that involves attaching expanded metal plates to the exsisting wall??

Martron Registered User

you will want to tie the walls together. depends on the type of construction. what you building?

RKQ Registered User

You can buy stainless steel anchor bars in most hardware stores.

A channel is fixed vertically to the existing wall, stainless steel "L" plates fit horizontally into this vertical channel. The "L" are placed every second row of new blockwork, according to manufacturers spec.
Easy and very strong solution. ( Not sure I can mention manufacturers name!)

Cutting existing blocks out is difficult, messy and could weaken the existing blockwork!

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FOXFISH1 Registered User

Yea Matron, thought as much...
Building an extension with cavity wall construction, ie 2 leaves of 100mm blockwork with insulated cavity.
Do i also need to tie in the footings?
Was hoping there would be another way, as having to tie in to the existing walls will mean having to remove a large existing window, very early in the project, in order to tie in properly

Just seen ur post RKQ, thanks, i shall further investigate this at the hardware stores

Martron Registered User

footings is easy. drill in dowel bars. very common solution. main thing is to ensure footings will not settle. ensure correct backfill is used and correst method of compaction. you will inevitably get some settling but this can be minimise with good practice.

as for the wall ties RKQ has a good solution. there will probably be many brands as its a common system

hope this helps

lots of systems though. all do the same thing. but as i say depends what you are building and the stress involved as in 2 storey etc etc

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RKQ Registered User

Good link above. Is it a two storey extension?

Use SDS drill to drill 12.5mm dia. holes at 150mm centres. Make sure you drill at 75mm minimum from bottom of conc. foundation. Drill holes as deep as possible in side of foundation, at least 200mm if possible.

Insert 12.5mm dia. steel bars. Tie these bars to A393 mesh, if using same in new foundation.

Ideally new foundation will be at least the same depth as existing foundation. I recommend at least 1000mm deep trench, subject to soil conditions. This depth avoids frost heave in winter and soil shrinkage in summer! It also works out to block dimensions / heights, 300mm thick conc. foundation, 3 rows of blocks to top of floor.

If new foundation is deeper that existing, drill 300mm deep vertical holes into foundation, then dig out (by hand) 600mm - 900mm under existing foundation. This creates a "step" in foundations with a good overlap. Homebond manual as a diagram and calculation!

Bend bars ( L shape) up into existing foundation holes. Tie bars to new steel reinforcing. Pour new foundation asap, perferably same day as digging under exist foundation.

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FOXFISH1 Registered User

Thanks Martron/RKQ ye have eased my worries!

Looks like i might be able to use the above system(or similar) and also possibly ensure continuity of the existing cavity with the new cavity.
(btw its a single story extension)

Martron Registered User

dont worry about it fairly handy stuff. problem is damp egress. make sure your dpc lines up with existing and ensure you have no damp bridges. if you can build lego you can build this.

good luck

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FOXFISH1 Registered User

I think i got my terminology slightly mixed-up.
What i meant to say was do i need to tie in the rising walls. ( i thought the rising walls were called footings, sorry).

Unfortuinately i already have the foundations in, and they are not tied to existing as such, however, the existing founds were 900 to their top surface so i just used this level as the bottom surface of new foundations. So the new foundations overlap the existing foundation.
I'm slightly worried about this now as i havn't allowed for differential settlement.
The new founds have the a393 mesh and also the ground is very solid.

Martron Registered User

900 deep should be grand and with the mesh ( raft ?) as long as you tie the next availible course to the wall you should be fine. but they def have to be tied. you should be grand follow specs of system. now the specs are in an ideal worls. if you missed the first 3 courses no major worries. just catch the rest of them.

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FOXFISH1 Registered User

Thanks a mil for your inputs...

Martron Registered User

no probs. sure if you have any other questions just ask ha ha

construct06 Registered User

not tying in the foundations is good as you have allowed for differential settlement between both the existing and new build.

to connect the new blockwork to the existing walls there is a fixing available using a bolted on vertical metal fing which has a slot for insering a tie. the correct tie to use here is one with a rubber around the end of it. the rubber is bedded in the mortar but the metal tie inside can move slightly if needed, again to allow for differential settlement.

remember that your existing house has settled over may years and your new build has a bit of catching up to do.

for the vertical metal fixing


the one referenced pp21 is the one you want i think...

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