Measurement Tolerances: Design vs Build

[Gaf]

24 minutes ago, joe90 said:

Quite, builder made a mistake, how he made that mistake is not relevant, you have proof in your drawings. You need (IMO) to point this out to them/him/her. Practically the only solution/compromise is reduce the service void rather than knock a concrete floor out. As a matter of interest what is the height of the upper floor? Is that one accurate? 

 

I was so focused on another issue (posted elsewhere about dot dab approach to plasterboard) that I didn’t measure the upper floor. The upper floor also hasn’t gotten the actual floor in yet (insulation, UFH, screed) bar concrete slabs. Plan to get a measurement in ASAP.

[saveasteading]

6 hours ago, Gaf said:

Each cross-section construction drawing includes the 255 measurement.

I think that's clear enough. It would have helped the builder to give the wall height under the upper slab, but perhaps that depended on the choice of plank.

NO, it is clear enough and it is a mistake. the ceiling had been made too low. Politely ask him to sort it.

 

You should run through the rest of the first floor construction too.  plank depth, and screed depth.  Remember that the planks have an upward  curve so the screed varies.

[saveasteading]

11 hours ago, Gaf said:

insulation, UFH, screed

Looking at the drawing again I notice that the service void and floor above slab  dims are given as 185mm and 100mm. This leaves 165mm for the plank at its highest point but may also include the ceiling thickness...that isn't clear.

I now think the builder may have some level of excuse. 

 

It isn't standard to have insulation and ufh upstairs. 

The insulation will prevent any bond between slab and screed.

Normally a plank needs the screed fof stiffness but your span is not long.

 

Please confirm that these are precast planks, aboug 1m wide that were craned or forklifted into place.

 

And who did this drawing?

[Gaf]

56 minutes ago, saveasteading said:

Looking at the drawing again I notice that the service void and floor above slab  dims are given as 185mm and 100mm. This leaves 165mm for the plank at its highest point but may also include the ceiling thickness...that isn't clear.

I now think the builder may have some level of excuse. 

 

It isn't standard to have insulation and ufh upstairs. 

The insulation will prevent any bond between slab and screed.

Normally a plank needs the screed fof stiffness but your span is not long.

 

Please confirm that these are precast planks, aboug 1m wide that were craned or forklifted into place.

 

And who did this drawing?

 

Drawing done by an Architect firm (actual architect, RIAI). 

 

Forgive my lack of knowledge on the terms. I’m not sure what dims or planks are.

 

The upper floor is precast concrete slabs (planks?) that required a crane to install. They are all 1.2m wide.

 

 

 

 

Edited December 30, 2024 by Gaf
Measurement wrong: slabs are 1.2m wide not 1.5m wide.

[Gaf]

@saveasteading As best I can calculate, excluding the precast concrete the build-up of the ceiling / first floor comes to 297.5mm, leaving 152.5mm for the precast concrete. 

 

[Russell griffiths]

Dims, means dimensions 

 

planks is the precast concrete slabs, floor structure. 

[saveasteading]

26 minutes ago, Gaf said:

leaving 152.5mm for the precast concrete. 

Apologies fof the abbreviations.

What do the planks/ slabs look like? Are they  plain concrete above and below and have hollow cores along the middle, now perhaps out of sight.?

These usually curve up and are about 25mm higher at the centre. Thus the makeup above will vary.

But occasionallh they are flat and my concerns would be unnecessary. 

 

Do you set the screed thickness at the low or high point? That shouldn't be your decision.

The drawing should state the specification  /supplier  and consider my concerns .

 

I suggest you check the depth available above. Either yourself with a spirit level or get someone else to do it.

 

Sorry, there's quite a lot of unknown. It may be no worry but the architect has been vague, or maybe  it is shown elsewhere.

 

 

[Gaf]

51 minutes ago, saveasteading said:

Apologies fof the abbreviations.

What do the planks/ slabs look like? Are they  plain concrete above and below and have hollow cores along the middle, now perhaps out of sight.?

These usually curve up and are about 25mm higher at the centre. Thus the makeup above will vary.

But occasionallh they are flat and my concerns would be unnecessary. 

 

Do you set the screed thickness at the low or high point? That shouldn't be your decision.

The drawing should state the specification  /supplier  and consider my concerns .

 

I suggest you check the depth available above. Either yourself with a spirit level or get someone else to do it.

 

Sorry, there's quite a lot of unknown. It may be no worry but the architect has been vague, or maybe  it is shown elsewhere.

 

 

 

Oh no hassle, just wanted to make sure I was getting it right 👍

 

They are plain concrete above and below with hollow cores. Can’t see them from below anymore. I recall noticing some, but not all, didn’t sit onto the internal walls and there was a gap. As in, they were sitting on the internal leaf of the external walls, but some weren’t sitting on the internal walls. This may suggest they were bowed.

 

Would this more impact the first floor than ground floor ceiling heights? Even taking the 25 bow, would this mean at worst the ground floor’s floor to ceiling height would lose the 25. So instead of 2550, it would be 2525 and not the current 2470?

 

 

 

Edited December 30, 2024 by Gaf

[Gaf]

2 hours ago, saveasteading said:

Apologies fof the abbreviations.

What do the planks/ slabs look like? Are they  plain concrete above and below and have hollow cores along the middle, now perhaps out of sight.?

These usually curve up and are about 25mm higher at the centre. Thus the makeup above will vary.

But occasionallh they are flat and my concerns would be unnecessary. 

 

Do you set the screed thickness at the low or high point? That shouldn't be your decision.

The drawing should state the specification  /supplier  and consider my concerns .

 

I suggest you check the depth available above. Either yourself with a spirit level or get someone else to do it.

 

Sorry, there's quite a lot of unknown. It may be no worry but the architect has been vague, or maybe  it is shown elsewhere.

 

 

 

Only dawned on me, with 152.5cm left for the precast slabs, and if the typically bow 25mm, then it would suggest the architect did allow for this bowing?

[saveasteading]

15 minutes ago, Gaf said:

suggest the architect did allow for this bowing?

I would never assume such a thing. 

 

If they knew, then the notes would tell you where the screed was to be thicker or thinner.

 

For example. Place insulation directly on the surface and lay screed to  minimum thickness x at the centre and to the same level to the remaining area.

 

Have you been up there ? Try jumping hard on the centre of one plank to check it doesn't bounce. Don't panic if it does just report.

 

Nobody has joined in the common discussion of whether you need insulation on an upper floor.

[saveasteading]

2 hours ago, Gaf said:

This may suggest they were bowed.

No, they bow at the factory when they are cut to length from one enormous plank. They will lose a few mm length at most.

 

I think they should all be on the inner leaf so that no damp cones from outside.

[Gaf]

On 29/12/2024 at 21:05, joe90 said:

 As a matter of interest what is the height of the upper floor? Is that one accurate? 

 

Upper floor is spot on. Current measurement of 2650mm with 100mm floor to go in, bringing it to 2550. 

 

On 30/12/2024 at 13:39, saveasteading said:

I would never assume such a thing. 

 

If they knew, then the notes would tell you where the screed was to be thicker or thinner.

 

For example. Place insulation directly on the surface and lay screed to  minimum thickness x at the centre and to the same level to the remaining area.

 

Have you been up there ? Try jumping hard on the centre of one plank to check it doesn't bounce. Don't panic if it does just report.

 

Nobody has joined in the common discussion of whether you need insulation on an upper floor.

 

Got a visit in. No movement in slabs when jumping (and Im heavy). The first floor walls are all done (concrete blocks throughout), so not sure if they are preventing any movement.

 

Got more measurements. The mf ceiling is extremely thin, approx 15mm. Based on the plans, the base of the slabs should be sitting on blocks at a height of ~2762.5mm. This allows 2550 ceiling, 12.5 plasterboard, 15 for the CF ceiling channel, and 185 service void.

 

Block work stops at ~2720, so ~42.5mm too low. The service void is 220, so ~35mm too low. Totals ~77.5mm too low.

 

[Gaf]

Quick addition to this. How would you feel about losing 2.5cm per wall to the plasterboards?

 

Checked plans agains wall to wall measurements, and they’re off by 2.5cm per wall. As in, our hall is 120cm wide in plans and is now 115cm. One bathroom is 170cm wide on plans and is now 165cm.

[DevilDamo]

44 minutes ago, Gaf said:

our hall is 120cm wide in plans and is now 115cm. One bathroom is 170cm wide on plans and is now 165cm.

Were the stated dimensions to the structure or finishes? If the former, then the 25mm would make sense for dot and dab or similar. A minimum of 1700mm between finishes is

common for a Bathroom to accommodate a standard bathtub.

[Gaf]

1 minute ago, DevilDamo said:

Were the stated dimensions to the structure or finishes? If the former, then the 25mm would make sense for dot and dab or similar. A minimum of 1700mm between finishes is

common for a Bathroom to accommodate a standard bathtub.

 

Dimensions were to finishes, not structure.

[DevilDamo]

12 minutes ago, Gaf said:

 

Dimensions were to finishes, not structure.

Well you need to speak to the contractor and find out the reasons behind the discrepancies. You should also raise it with your Architect. 

[Gaf]

On 01/01/2025 at 21:59, DevilDamo said:

Well you need to speak to the contractor and find out the reasons behind the discrepancies. You should also raise it with your Architect. 

 

Figured it out. Architect plans didn’t include a depth for battens or dot-dab. Waiting on a reply from on why. At present I can only surmise they intended the IWI to be affixed directly onto blockwork.