Mixing methods of Blockwork construction?

RKQ

I have always understood the benefits of standard cavity wall construction i.e 100mm solid external block, 40mm air gap, cavity insulation and solid internal 100mm wide block.

I know 215mm solid blocks laid flat and drylined internally, has been standard in Dublin area for many years. But the lack of / detailing dpcs to heads and reveals can be problematic.

I do allow 215mm hollow block construction for domestic garages or garden sheds. This construction has no real insulation value.

I don't see how it is possible to marry a 300mm cavity block wall to a 215mm soild blockwork wall, especially at the corners. Render would provide a certain protection but clay brick tied to solid blocks is impossible!
There are serious insulation problems with this marriage but the possibility of damp penetration is also high.

Has anyone come across this marriage or been able to "retro-fit" an acceptable solution to wall insulation (cold bridge) and damp problems at the corners?

topcatcbr

RKQ wrote: »

I have always understood the benefits of standard cavity wall construction i.e 100mm solid external block, 40mm air gap, cavity insulation and solid internal 100mm wide block.

I know 215mm solid blocks laid flat and drylined internally, has been standard in Dublin area for many years. But the lack of / detailing dpcs to heads and reveals can be problematic.

I do allow 215mm hollow block construction for domestic garages or garden sheds. This construction has no real insulation value.

I don't see how it is possible to marry a 300mm cavity block wall to a 215mm soild blockwork wall, especially at the corners. Render would provide a certain protection but clay brick tied to solid blocks is impossible!
There are serious insulation problems with this marriage but the possibility of damp penetration is also high.

Has anyone come across this marriage or been able to "retro-fit" an acceptable solution to wall insulation (cold bridge) and damp problems at the corners?

I dont understand why you would want to do this. But the entire external wall area could be drylined with insulated slabs as im sure you are aware of. Brick reinforcement matt could be used in the joint to strengthen this area.

Not a detail i would use.

RKQ

I don't want to marry the two methods.
I think it goes completely against the grain and I can't understand why someone would marry the methods.

If you can across a cavity wall tied to a solid gable wall, would you have the gable demolished and rebuilt as a cavity wall?

Quazzie

It might be cheaper and more stable to build a 100 inner leaf on the Gables installing Insulation as you go, thus resulting in 215 outer leaf 40 cavity Insulation and 100 Inner leaf, Or indeed vice versa by building an outer leaf. Although not ideal it is possibly a better solution than knocking the gable, and all the hassle that it brings with it.

It would require some careful detailing at the corner and some careful demolition and rebuilding but it should be ok if done right.

sydthebeat

RKQ wrote: »

I don't want to marry the two methods.
I think it goes completely against the grain and I can't understand why someone would marry the methods.

If you can across a cavity wall tied to a solid gable wall, would you have the gable demolished and rebuilt as a cavity wall?

you get this issue with 310 cavity anyway....

the outer leaf of a 2 storey gable becomes and internal wall where it meets a single storey construction.
Personally i would insulate the cavity block in the attic void, if there is one. Its much easier than rebuilding a gable.

to be honest, if you are building to a high degree of energy efficiency you will detail this problem out..... if your not... then the necessity diminishes.

regarding building a cavity wall against a cavity block wall... again, you get the same problem with an extension to a cavity wall, the outer leaf becomes internal.

topcatcbr

RKQ wrote: »

If you can across a cavity wall tied to a solid gable wall, would you have the gable demolished and rebuilt as a cavity wall?

I dont know the scale and context but it is unnecessary to demolish solid gable. Adding an internal/external leaf sounds good but may require underpinning. I think i would dryline all external walls and detail as if they were cavity block construction. see page 58 HB manual 6th edt. the joint between the two could be treated as a movement joint tieing the internal leaf to solid block and joining external leaf see p 93 to 102 particularly p 98.

Slates

sydthebeat wrote: »

you get this issue with 310 cavity anyway....

the outer leaf of a 2 storey gable becomes and internal wall where it meets a single storey construction.
Personally i would insulate the cavity block in the attic void, if there is one. Its much easier than rebuilding a gable.
.

Do you mean where a 2 story part of a building goes through the roof of a lower part of a building where the cavity is brought into the building ???

sydthebeat

Slates wrote: »

Do you mean where a 2 story part of a building goes through the roof of a lower part of a building where the cavity is brought into the building ???

yes...

Slates

sydthebeat wrote: »

yes...

Would you fix plaster/laminate board to the outer/now inner blockwork ?

sydthebeat

Slates wrote: »

Would you fix plaster/laminate board to the outer/now inner blockwork ?

depends what way the ceiling of the single storey is constructed.

Its become very popular to put raised ceilings, or even 'open to ridge' type in single storey outcrops.... if this is being done the yes, definitely use composite plasterboard as an insulator.

If its a standard flat ceiling type what i recommend is, along with the usualy 300 quilted on the flat ceiling and the 60mm in the cavity, to place another 300-400mm of board insulation at the ceiling level to fill the cavity... therefore the concrete head (and block over)are surrounded on two sides with insulation.... thats enough IMO.... Alternatively use a full fill top hat section intel....