Block on flat inner leaf

Splinter Cell

Been thinking thru' block on flat inner leaf for cavity wall some more .....
Had assumed that standard block size is 440 x 215 x 102.5 but measured is actually 440 x 215 x 100. Assuming 10mm for mortar, first 2 courses of block on flat inner leaf is 10 + 100 + 10 +100 = 220mm. First course of outer leaf is 10 + 215 = 225mm. Won't this cause a wall tie to be tilted downward? :eek: By the tenth outer course, the outer mortar is facing straight into the centre of an inner leaf block. Does this method rely on the block layer applying 2.5mm more mortar on each inner course?
Hope this isn't a dumb question, my day job works in microns and 5mm seems like something a truck turns in!

Poor Uncle Tom

The AVERAGE size of a block is 440 x 215 x 100 and its size in a finished wall, including mortar joints, for m2 calcalations is 450 x 225, but these are average sizes. I've seen blocks at 430 and 450 long and 220 and 230 high. Does this mean they're rejected, no, there is extra or less mortar used in the jointing to compensate.

It's exactly the same in the case you describe, thats why lines, hammers, tapes and levels are used in laying the courses. There's nothing strange in making a mortar bed extra heavy or tamping some out to get the required level.

Splinter Cell

Thanks Poor Uncle Tom! Thought as much but just checking.
Am leaning very much towards this type of construction. I assume this inner leaf can support the roof structure so can the roof be installed before the cavity insulation and outer leaf are fixed?

kavoweb

i presume you just mean the roof trusses,if so,then of course it will support them just fine.....are you on a self build?? nosy,eh.

Splinter Cell

kavoweb wrote: »

i presume you just mean the roof trusses,if so,then of course it will support them just fine.....are you on a self build?? nosy,eh.

Yes, meant the trusses, L plates on at the moment but learning fast.
Will hopefully be starting self build soon, just got PP but house drawings are not up to date. Hired engineer to update with better insulation, UFH, air tightness, HRV, etc. + do relevant DEAP, BER and site supervision etc.
Must keep overall proportions and appearance of house of course but coco. want ground to ridge height reduced to < 7M and this proving to be a problem. A rough calculation:
0.2M to finished floor
2.6M to ceiling
0.3M first floor
2.5M to ceiling
~0.3M rafters
~0.3M for trusses @ 30d pitch
This leaves ~0.8M for attic, can't even fit a standard water tank in.
Anybody have a similar experience? Can't understand the coco. logic, house next door was granted 7.5M high

Poor Uncle Tom

Splinter Cell wrote: »

........... I assume this inner leaf can support the roof structure so can the roof be installed before the cavity insulation and outer leaf are fixed?

Yes, this 225mm inner leaf will support the roof and yes the roof can be installed before the insulation and outer leaf are fixed. I prefer to bring up both leafs together purely because it is much easier to clean the mortar from the rear of the second leaf if you can lean over the first one to do it. I used the 225mm inner leaf a good few times during the 1980's because a concrete first floor needed the space for support at that time and found great benefits from them, so it's not new, and it is proven.....:)

Carlow52

SC: are u double counting the 0.3 for rafter and roof truss as the normal construct is that the collar in the truss is the ceiling rafter.

Re doing the roof before the outer leaf just remember that the rafters will overhang the outer leaf by .3 or 0.4m at an angle which will make the top few outer leaf courses tough to do and will make closing the cavity 'tough'

Splinter Cell

Poor Uncle Tom wrote: »

Yes, this 225mm inner leaf will support the roof and yes the roof can be installed before the insulation and outer leaf are fixed. I prefer to bring up both leafs together purely because it is much easier to clean the mortar from the rear of the second leaf if you can lean over the first one to do it. I used the 225mm inner leaf a good few times during the 1980's because a concrete first floor needed the space for support at that time and found great benefits from them, so it's not new, and it is proven.....:)

My thinking here (based on what I have read on this forum) is to mitigate against thermal looping by building up the internal leaf with wall ties protruding first. Install roof. Ensure wall face level, no mortar protruding etc. Fit extruded 100mm PS below DPC, PIR board above. Ensure joints tight and tape, all DPC present and correct at opes. Then build outer leaf.
Just to be sure, could I fully complete the roof before the insulation, outer leaf build?

Splinter Cell

Carlow52 wrote: »

SC: are u double counting the 0.3 for rafter and roof truss as the normal construct is that the collar in the truss is the ceiling rafter.

Sorry, need to brush on my terminology. Assuming 0.3M for the ceiling rafter and 0.3M for where the roof timbers @ 30d pitch meet.

Carlow52

okay, the second 300 is the ridge board:)

Again consider how u will close the cavity on top if the roof joists are in place before u build the outer leaf

Jimbo

Would a one and a half storey house be accetable at that location?

You could still retain 1.6-1.8m head height at the sides and make the attic more useable.

It can also add character to a house.

V6DEC

Splinter Cell, I'm currently 3/4 the way up with a two story self build with the inner leaf on the flat. Wall constriction from Inside to Ourside is 215(block on the flat), 150mm cavitiy (100mm Kingspan Insualtion + 50mm moisure gap) and Outer leaf is 100mm (Red-brick),,, front of the house is the same but redbrick is replaced by a block on the edge with expanding metal ready for 8" Natutal Stone. It's definately worth it,,,we've also built most of the internal walls on the flat the whole way up and this is allowing us to put precast on both the 1st floor and on the attic floor (which will be handy for conversion in the future!). It also makes the roof very simple was we plan to built a 4ft wall on the attic floor a few feet in from the edge wand this will act as a purlin onto which the roof will be tied onto. We have decent reveals around the windows and doors but plan for twice as much blocks and sand/cement...We're already on the 26th load of 4"....but nearly there:).

Splinter Cell

Carlow52 wrote: »

okay, the second 300 is the ridge board:)

Again consider how u will close the cavity on top if the roof joists are in place before u build the outer leaf

Spent the afternoon discussing this with the builder (brother in law). You are all right about the cavity closer. Will leave this one to the engineer for next week, but will most likely have to leave the roof off until the outer leaf is built.

Splinter Cell

Jimbo wrote: »

Would a one and a half storey house be accetable at that location?

You could still retain 1.6-1.8m head height at the sides and make the attic more useable.

It can also add character to a house.

[FONT=Verdana, sans-serif]Hi Jimbo,[/FONT]

[FONT=Times New Roman, serif][FONT=Verdana, sans-serif]The house is one and a half story, 8.4M gable with 100 outer leaf, 140 cavity w/ 100 PIR and 215 inner leaf wall. Sorry for the crude side elevation drawing attached, CAD file is on my work laptop and I decided to leave work at work for the long weekend. [/FONT][/FONT]

[FONT=Verdana, sans-serif]Don't think I will get much use out of this attic, will ensure to keep HRV unit close to trap door for filter changes etc.[/FONT]

Splinter Cell

V6DEC wrote: »

Splinter Cell, I'm currently 3/4 the way up with a two story self build with the inner leaf on the flat. Wall constriction from Inside to Ourside is 215(block on the flat), 150mm cavitiy (100mm Kingspan Insualtion + 50mm moisure gap) and Outer leaf is 100mm (Red-brick),,, front of the house is the same but redbrick is replaced by a block on the edge with expanding metal ready for 8" Natutal Stone. It's definately worth it,,,we've also built most of the internal walls on the flat the whole way up and this is allowing us to put precast on both the 1st floor and on the attic floor (which will be handy for conversion in the future!). It also makes the roof very simple was we plan to built a 4ft wall on the attic floor a few feet in from the edge wand this will act as a purlin onto which the roof will be tied onto. We have decent reveals around the windows and doors but plan for twice as much blocks and sand/cement...We're already on the 26th load of 4"....but nearly there:).

Hi V6DEC,
26th load ..... ouch! Sounds like a great build though, best of luck with your new home, may be pm'ing you some day when the insanity sets in.
BTW, did you complete the inner and outer leaf together or separately as I am planning to do? Would love to hear from anybody who has done this .....

Carlow52

Splinter Cell wrote: »

Spent the afternoon discussing this with the builder (brother in law). You are all right about the cavity closer. Will leave this one to the engineer for next week, but will most likely have to leave the roof off until the outer leaf is built.

Glad to be of help: having seem the gable detail, u will have to do outer leaf before u roof the gable

Graaaaa

Hi Splinter,
I am suggesting a proprietary precast roof overhang which may allow you to build your outer leaf later. I have not had any experience of it as yet myself, but I have been chatting with them and I can't find fault, very helpful guy.
Maybe give them a call and discuss what you're trying to do? Website has CAD details to download too, should help you make a better assessment.
No idea of cost comparison, I expect it's going to be more than the last block of outer leaf + soffit + fascia, but in terms of lifetime costs the sales pitch is that there's no maintenance required.
I'll PM you the link in case this oversteps the charter.

Splinter Cell

Graaaaa wrote: »

Hi Splinter,
I am suggesting a proprietary precast roof overhang which may allow you to build your outer leaf later. I have not had any experience of it as yet myself, but I have been chatting with them and I can't find fault, very helpful guy.
Maybe give them a call and discuss what you're trying to do? Website has CAD details to download too, should help you make a better assessment.
No idea of cost comparison, I expect it's going to be more than the last block of outer leaf + soffit + fascia, but in terms of lifetime costs the sales pitch is that there's no maintenance required.
I'll PM you the link in case this oversteps the charter.

Thanks Graaaaa, PM received. This is a novel idea, I will give them a call and see if this will allow me to build the outer leaf after the roof goes on.

Talking to engineer last night, he agrees with block on flat inner leaf first to ensure proper installation of the PIR boards. In fact, he also suggested glueing the boards to the inner leaf to really ensure air tightness. Sounds like a good idea to me .....