Precast 1st floor

briaineo

Hi

I am going with a precast 1st floor in a new build, since most of the first floor will be bedrooms; whats the process if I wish to lay carpet in the rooms do I put down a wooden sub floor first?

thanks

SC024

No need, you have your precast slabs then underfloor heating if fitted & screed poured over & then lay your Underlay & carpet over this.

briaineo

thanks

that solves one question but creates another!

I wasn't going with under floor heating just plain aul rads, since a sub floor or screed (just need to grout the joints) isn't required whats the best option for concealing the piping for the rads?

Behind the skirting? Which would work fine if the pipes were not insulated using the normal type anyway.

Not going with insulated plasterboard just the standard 12mm one.

Is there a concrete block available with a notch / groove in it that would take part of the pipe?

Or a slimmer type of pipe insulation than the standard foam one?

OR am I over thinking this and there is plenty of room between the wall and skirting?

galwaytt

The precast slab isn't flat, it's cambered, so you will have to put in a level screed anyway. Treat it as per your GF slab and insulate it and pour screed over. Put your insulated pipework in that dimension - you can't fit it as you describe to the walls.

Metric Tensor

If you are using rads in my opinion it is pointless insulating the first floor slab.* Just put a screed on top of it (NB the shear keys) and put your pipes in the screed the same as downstairs.

As galwaytt says you will need a screed anyway because the tops of the slabs will be rough and cambered. Also don't forget to factor this screed into your stairs calcs.


* Even with UF the need for insulation at first floor level is a subject of debate.

Calahonda52

briaineo wrote: »

.....

Not going with insulated plasterboard just the standard 12mm one.

....

Having read this, just wonder whats the rest of the construction like.
Where is the A?T layer.
Are you using MHVR?
Whats the wall/roof makeup, including insulation?

briaineo

Calahonda52 wrote: »

Having read this, just wonder whats the rest of the construction like.
Where is the A?T layer.
Are you using MHVR?
Whats the wall/roof makeup, including insulation?

Hi

The walls are standard cavity with 150mm pumped bonded bead, the flat roof will be of fibreglass and insulated with most likely a combination of rockwool and insulated plasterboard; although have to research this more. The ground floor insulation will be 100mm board.

As per the 12mm plasterboard, not using an insulated board inside as this should only be used for existing buildings and not new builds. Theres plenty of threads advising against using insulated board on a new build indoors.

Don't think i'm going with a MHVR system this could change.

not sure what the A?T layer is?

Calahonda52

A/T, my bad: airtightness layer.

Why use the board at all then?

The two ideas, A/T and the board are connected.
How will the board be fixed?
whats the plan for electrical and other services.

Re
"Don't think i'm going with a MHVR system this could change."

You need to think about this, especially for drilling holes through the precast floors.

Standard cavity wall c/w 150 mm cavity with pumped beads with precast floors: who did the bearing load calculations for you?
How ill you stop the beads form blowing up the precast?

briaineo

Calahonda52 wrote: »

A/T, my bad: airtightness layer.

Why use the board at all then?

The two ideas, A/T and the board are connected.
How will the board be fixed?
whats the plan for electrical and other services.

Re
"Don't think i'm going with a MHVR system this could change."

You need to think about this, especially for drilling holes through the precast floors.

Standard cavity wall c/w 150 mm cavity with pumped beads with precast floors: who did the bearing load calculations for you?
How ill you stop the beads form blowing up the precast?

Thanks for the response

Actually decided against the mechanical ventilation.

On the air tightness: could go with a membrane but was reading that plastering suffices as a a/t layer but do you think slabbing would reduce this effectivity?

Was going with the plaster slabs battened to avoid the colder wall feel. And make it easier for running wiring etc.

I never even thought that the beads would blow up the hollow core. Although there must be a solution to this. If I can manage to use the boards at a similar price I will.

Hadn't sorted out the load bearing calculations yet with the engineer, but have spoken with suppliers / fitters of the precast and was working off their guide for the walls; no wall spans more than 5m and 100mm to rest on. There will be a wall on the flat running down the centre of the house which will allow 100mm resting point for each where both slabs meet.

Thanks again for the advice new to all this but trying to take in as much info as I can.

Metric Tensor

briaineo wrote: »

Hadn't sorted out the load bearing calculations yet with the engineer, but have spoken with suppliers / fitters of the precast and was working off their guide for the walls; no wall spans more than 5m and 100mm to rest on. There will be a wall on the flat running down the centre of the house which will allow 100mm resting point for each where both slabs meet.

Who is designing the foundations under the walls? Who is giving the roof and upstairs loading calculations to the slab designer and who is checking their design is sufficient?

With regards to slabbing the external walls - you will need to plaster the wall first and then put the slab up if you want to use a plaster layer as your air-tightness layer or else put a membrane behind the slab. My advice would be to forget about the slabbing.

Also I'd strongly review your "decision" re MHRV. Have you asked the person doing your DEAP calculation what air-tightness value is necessary to meet your Part L obligations. If it's on the low side the house will be stuffy and poorly ventilated without MHRV.

Calahonda52

Me thinks there is an element of penny wise , pound foolish about this project.

Have u done the Life cycle "math" on the MHVR?

On what basis have u decided against it?

Have u speken to anyone who has one?

You have a once-off chance to make this house a very energy efficient and very comfortable house so don't blow it.

Re: the A/T layer have u read about cement plaster or gypsum skim?

Service ducts behind plaster board, without carefully working out the location of the A/T layer and minimising, or ideally eliminating any A/T penetrations by the services requires careful planning and much attention to detail.

There is much much more to it than "And make it easier for running wiring etc"

You just cannot have the trades, with their core drills , making Swiss cheese of the A/T layer.

Do you play golf?

Do you drive?

MicktheMan

Calahonda52 wrote: »

Me thinks there is an element of penny wise , pound foolish about this project.

Or knowing the price of everything and the value of nothing.

cork2

First things first. You MUST put a screed on precast floors even if it's very thin, as in a lot of cases as said there's a camber in the slabs but also in an awful lot of cases if you go through the spec provided by the precast company it will state that the slab doesn't reach it's full strength and become a structural deck until there is a screed on it.
As for the cavity beads blowing into the precast slabs, talk to the manufacturers they can block the ends. An extension I'm doing at the moment all the precast slabs have the ends filled coming.
Before you go too far talk to your engineer, I can't emphasise this enough. Also as for the screed your engineer will be telling you what screed you're putting on it as apposed to you telling him.
Your engineer will also be telling you whether 100mm bearing on the walls is enough. In most cases I've seen there's 225mm bearing and steel lintels over all the windows downstairs where you have precast above. I hope all these loadings were also taken into account underground at the foundation?
Whatever you do get your engineer to meet you on site walk the house and get him to explain how the structure comes together, make sure he's happy with everything on the ground floor before you drop in precast slabs and don't order slab without showing him what it is you're buying. After all these things are what he does. Whilst the internet is great for opinions and meeting people who have been there and done it your engineer is the guy calling the shots when it comes to structure. Never take a chance and if you're unsure ask.

briaineo

Thanks

I have reconsidered the mechanical heat ventilation and will be installing this system.

I did speak with the precast company; this is probably my fault for not quoting the material correctly: what I was told by the company was: if I went with prestressed all that was grouting the joints and if I went with other product they had a structural screed was required. Both came I at the same price but they said a small reduction could be made to the product requiring a screed. They also mentioned that the prestressed is laid on a 100mm resting point and block on the flat where 2 slabs meet.

I do take your points regarding the camber and a screed is required to level out the camber.

The roof will have a minimal load bearing when compared to the a standard slate roof. Going with a fibreglass flat roof.

What I was hoping to do regarding the engineering of the build: was to figure out as much of the calculations as I could first and let him fix the inaccuracies. Or just bin it and let him start from scratch! Either way hopefully I'll learn something along the way.

We haven't managed to get the perc test done in the weather were having, which was due to be done before Christmas. Plus we have to transfer the site before we apply for planning (far from the usual scenario don't buy a site before planning)

Metric Tensor

briaineo wrote: »

The roof will have a minimal load bearing when compared to the a standard slate roof. Going with a fibreglass flat roof.

Have you checked the snow drift loading at your site and the wind uplift for all 9 zones on the roof to back up your analysis that it is less than for a pitched roof over a similar area? Have you given these take down loads to the precast manufacturer to include in their design?

briaineo wrote: »

What I was hoping to do regarding the engineering of the build: was to figure out as much of the calculations as I could first and let him fix the inaccuracies.

Have you ever been to hospital - did you do a fair bit of the surgical procedure yourself in advance?

Your engineer has many years of training and experience as well as most importantly insurance backing his designs and analyses. Unless you are intimately familiar with IS EN 1991 and IS EN 1996 (to start with) it would be madness to think you can do the calculations yourself.

galwaytt

Metric Tensor wrote: »

Have you checked the snow drift loading at your site and the wind uplift for all 9 zones on the roof to back up your analysis that it is less than for a pitched roof over a similar area? Have you given these take down loads to the precast manufacturer to include in their design?



Have you ever been to hospital - did you do a fair bit of the surgical procedure yourself in advance?

Your engineer has many years of training and experience as well as most importantly insurance backing his designs and analyses. Unless you are intimately familiar with IS EN 1991 and IS EN 1996 (to start with) it would be madness to think you can do the calculations yourself.

on the subject of wind: ...we're fitting flat roof to a build in Ballyconneely this week. A windier, wilder spot you couldn't get. Even the main contractor on the job has the heebies about the wind out there. Uplift is the main culprit.

Metric Tensor

Particularly at the leading edges.

Be careful not to get caught out in the wind in Ballyconneely yourself or you might have to start posting as newyorktt next week!!!!

briaineo

Metric Tensor wrote: »

Particularly at the leading edges.

Be careful not to get caught out in the wind in Ballyconneely yourself or you might have to start posting as newyorktt next week!!!!

Luckily I've no leading edges!

Metric Tensor

In which case you have parapets - a snow drift attracting challenge that your engineer will explain to you.

briaineo

Metric Tensor wrote: »

In which case you have parapets - a snow drift attracting challenge that your engineer will explain to you.

Yep, it will be a factor alright, hopefully not too much of one.

Seems that having mechanical ventalation with a cold roof is a benifit.

galwaytt

briaineo wrote: »

Yep, it will be a factor alright, hopefully not too much of one.

Seems that having mechanical ventalation with a cold roof is a benifit.

I don't see any connection between ventilation of a building and whether the roof is cold or warm build up.

That said, I'd always build a warm roof.

Metric Tensor

Also the roof build up (cold vs warm) and ventilation have nothing whatsoever to do with snow and wind loading.

briaineo

Metric Tensor wrote: »

Also the roof build up (cold vs warm) and ventilation have nothing whatsoever to do with snow and wind loading.

Sorry misquoted something previously I should have said: a cold roof is better for snow but as you rightly said has no bearing on the load factor.

Metric Tensor

briaineo wrote: »

cold roof is better for snow

I'm not sure you know what is meant by a "cold roof" and a "warm roof."

You really need to get some expert advice and guidance. Who is doing your planning application?

galwaytt

briaineo wrote: »

Sorry misquoted something previously I should have said: a cold roof is better for snow but as you rightly said has no bearing on the load factor.

...er, no, I don't get that either: why is a cold roof 'better' for snow ? In what way ??

sydthebeat

briaineo wrote: »

Sorry misquoted something previously I should have said: a cold roof is better for snow but as you rightly said has no bearing on the load factor.

as is being said above..... ????? what do you mean here?
i think you might have your understandings a bit mixed up.


http://www.boards.ie/vbulletin/showthread.php?p=68250588

briaineo

galwaytt wrote: »

...er, no, I don't get that either: why is a cold roof 'better' for snow ? In what way ??

From why I found in a few different web sites was that a cold roof was more preferable in snowy conditions as it less susceptible to ice dams.

The warm roof with the a higher temperature closer to the outer roof structure melts the snow and allows ice dams to occur easier.

sydthebeat

briaineo wrote: »

From why I found in a few different web sites was that a cold roof was more preferable in snowy conditions as it less susceptible to ice dams.

The warm roof with the a higher temperature closer to the outer roof structure melts the snow and allows ice dams to occur easier.

we dont get the extreme temperatures that cause ice dams, plus, they are more of an issue on pitched roofs where water is designed to run off quickly but are trapped.

flat roofs are designed to be able to hold water until a slow run off.

anyway its very debatable whether a warm roof is worse than a cold roof for this. Id argue that a warm roof affords a more uniform melting sequence across a flat roof where a cold roof would have more pockets of ice /snow.

in all honesty, its not an irish problem. The heaviest snowfall we've had on record was 450mm (1 1/2 foot, back in '62) and thats miniscule compared to the snowfalls where ice dams are a factor (on average our snow fall depths are around 100mm)

briaineo

sydthebeat wrote: »

we dont get the extreme temperatures that cause ice dams, plus, they are more of an issue on pitched roofs where water is designed to run off quickly but are trapped.

flat roofs are designed to be able to hold water until a slow run off.

anyway its very debatable whether a warm roof is worse than a cold roof for this. Id argue that a warm roof affords a more uniform melting sequence across a flat roof where a cold roof would have more pockets of ice /snow.

in all honesty, its not an irish problem. The heaviest snowfall we've had on record was 450mm (1 1/2 foot, back in '62) and thats miniscule compared to the snowfalls where ice dams are a factor (on average our snow fall depths are around 100mm)

True alright,

Don't think the snow load is going to be a huge factor - also in the lowest area of snow on map in tgd's.

But the engineer will confirm the correct specs.

Metric Tensor

In a European context Ireland's maritime climate (and the UK) gives a unique set of wind driven snow conditions that are not experienced in heavier snowfall areas of the continent. Because of this there is a very specific set of snow loading codes for our environment. An engineer will know this and use the appropriate code for structural design of your roof but without knowing the ins and outs of it you won't find a whole lot of relevant information by googling.

I've never seen or heard of an ice-dam occurring in Ireland but sliding snow could have a similar structural effect which is accounted for in the drift loading parameters. As syd says though - that's a pitched roof issue. ALSO - if you are having parapets you've essentially built yourself a blockwork ice-dam anyway.

One last time - talk to a building professional sooner rather than later - a good one will teach you more in an hour than 3 months worth of googling. (If you are reading about ice-dams you are waaaaaaaay off the mark in terms of learning anything useful to your building in Ireland!)

galwaytt

briaineo wrote: »

From why I found in a few different web sites was that a cold roof was more preferable in snowy conditions as it less susceptible to ice dams.

The warm roof with the a higher temperature closer to the outer roof structure melts the snow and allows ice dams to occur easier.

...I'm sorry, and with all due respect, and I'm not trying to be mean or anything, but there is way too much internet in that statement..........it's time to take step back and get practical, real-world advice. Designing for ice dams in this country is simply so far away from where we are I don't know where to start.

Your comment about the warm roof bringing temperatures closer to the snow is similarly misguided.

Sorry

Calahonda52

Metric Tensor wrote: »

One last time - talk to a building professional sooner rather than later - a good one will teach you more in an hour than 3 months worth of googling. (If you are reading about ice-dams you are waaaaaaaay off the mark in terms of learning anything useful to your building in Ireland!)

My, my, my: how have we lost the plot here, with ice dams warm vs cold roof and such like, with ever facet having to be extracted by deduction as if its a secret to have a flat roof with parapets as opposed to overhangs et al

This quy here might help
https://www.youtube.com/watch?v=aQzlJRjXSGY

Or as Rhett said to Scarlett: Frankly, my dear, I don't give a damn: ice or otherwise.

Am all done here

THE DON FANUCCI

anybody know anything about wrapping the ends of precast slabs before installation? - is thisto help with airtightness or dampness ?? or is it to prevent air movement into the hollowcore?? will the bonded bead insulation not just block up the end of the hollowcore anyway or could i use expanding foam to block the hollow cores? any help appreciated

MicktheMan

THE DON FANUCCI wrote: »

1.anybody know anything about wrapping the ends of precast slabs before installation?
2- is thisto help with airtightness
3 or dampness ??
4 or is it to prevent air movement into the hollowcore??
5 will the bonded bead insulation not just block up the end of the hollowcore anyway
6 or could i use expanding foam to block the hollow cores?

1. Use the search function - this has been fully covered in the past
2. yes, to create a continuous barrier from downstairs to upstairs.
3. no
4. no
5. no
6. no

THE DON FANUCCI

But if I have a suspended metal ceiling and slabbing then onto that and skim coat then on that and internal plastered walls and skim coat up to ceiling on them.
Is this joint at the precast slab on the wall really losing alot of air ??

MicktheMan

Yep

THE DON FANUCCI

Ok. Where do I find an air tightness tester? And how much are they I wonder