How to build on a cast slab?

[stefankocken]

Hi!

I'm going to help my mom with an extension and we've decided that it will have a concrete slab foundation. I've done a lot of extensions on my own house, but those were on stilts, so I know how to do that properly.

But how does it work with floor joists and a concrete slab? Organic material should never touch concrete... Can anyone guide me on the layers from the concrete and upwards? How is it with ventilation, etc.? Insulation? Vapor barrier?

Thanks in advance/ Stefan

 

[SBH]

you use syllisolering.
then the construction often depends on what you have in the rest of the house.
do not mix

 

[stefankocken]

What is sill insulation? The house was built in 1936 with "stuff that was lying around," so avoiding mixing materials is completely impossible. Moreover, I don't see any problem with mixing constructions as long as they don't "depend on each other." In my own house, the old part is on a crawl space foundation and the new part is on piers.

 

[SBH]

you can search. you still have to look for materials.
if you start with plastic in the new part, you should use plastic in the rest

 

[stefankocken]

Is there any rule that says plastic in old houses? The reason old houses stand for so long is that the ventilation is superior as it airs itself automatically. In my own, I would never put a vapor barrier in the old part that has stood for 150 years.

 

[SnickarMartin]

Under all wooden sills, you can use regular construction plastic that you cut to size, or a strip of tjärpapp. There are also ready-made plastic rolls specifically for sill installation.

 

[stefankocken]

Is that really the only difference? Lay the sill on sill paper and build and insulate the floor structure as usual?

 

[Bödde]

Is that the only difference really? Place the sill on sill paper and construct and insulate the joists as usual?

The wall construction itself is the same regardless of what foundation you have?! The most important thing, as already mentioned, is to stop moisture from moving through the slab up into the sill. If it works technically, you can also lay a row of leca blocks to raise the framing a bit from the slab. On the row of leca blocks, you place the tar paper and then the sill.

 

[SBH]

Is that really the only difference? Place the sill on sill paper and build and insulate the joists as usual?

have you done any research yourself???

 

[stefankocken]

Of course I have, but the internet is messy as hell and you never get any particularly clear answers, I think. That's why I'm asking and hoping there is someone who can provide informative answers instead of questioning if one is lazy and doesn't bother to search for information... That's how I interpret your three question marks after your question.

 

[SBH]

seen it for example?
http://www.traguiden.se/konstruktio.../grundlaggning/platta-pa-mark/principlosning/
it is your responsibility in the end.
don't care how many question marks I put!

 

[Bödde]

seen it for example?
[link]
it's your responsibility in the end.
I don't care how many question marks I use!

But SBH, aren't we in a construction forum? Surely one can ask whatever they want?!

 

[SBH]

But SBH, we are in a construction forum, right? You should be able to ask whatever you want?!

yes of course. but there are so many good suggestions for the ts to look at.
there are even points on how to do it

 

[Bödde]

yes, of course. but there are so many good suggestions for ts to look at. there are even points on how to do it

You do have a point there. Good that you linked...

 

[SBH]

You are correct in that regard. Good thing you linked...

same thing. but no material against the concrete except for syllisolering