timber frame/ raft detail

slowharry

I am looking to build a timber frame house of a raft foundation. i was flicking through the homebound book and came across this detail (which i've roughly sketched).
The sole plate (cyan) seems to be above ffl and therefore above the dpm (red) and (dpc) blue. i hadn't really put much thinking into how this would work but it was along the lines of fixing the soleplate direct to the raft. it seems like there is a course of block work (green) required.
Is this neccesary or can treated timbers be used getting a block layer in for that will be a lot of hassle

Thanks

sydthebeat

you need a level to screed off, this is normally the top of this block course. you can use a full 215 block, incorporate 140 insulation and 75mm reinforced screed.

Why is it hassle? is the workmanship of the raft pour very bad?

slowharry

thanks for the reply syd

i haven't started on site yet just trying to get the ducks in a row first. i have a fair amount of groundworks and a lad lined up to do it, he also does rafts so instead of strips and rising walls i was going to get him to put in the raft. then timber frame company to come in on on top. starting tp findout that there is a bit more to it. just trying to avoid blocks as much as possible ( hassle). it might now make more sense to go with a strip footing and rising wall

thanks again

sydthebeat

if you have a choice between strip and raft, go for strip every time.

generally theres about a 2 to 1 cost difference between them.

only go for a raft if the ground conditions require it.

sprinkles

raft will def cost more and it's more hassle than strip.

Rising wall will req blockwork....

yop

slowharry wrote: »

I am looking to build a timber frame house of a raft foundation. i was flicking through the homebound book and came across this detail (which i've roughly sketched).
The sole plate (cyan) seems to be above ffl and therefore above the dpm (red) and (dpc) blue. i hadn't really put much thinking into how this would work but it was along the lines of fixing the soleplate direct to the raft. it seems like there is a course of block work (green) required.
Is this neccesary or can treated timbers be used getting a block layer in for that will be a lot of hassle

Thanks

Are you intending to put in your final floor as part of your raft?
What is your ground like, your engineer will decide on your foundation, what is he/she saying?
Your sole plate is tanalised timbers, ask your TF company for their requirements. You will have a min 2" sole plate.
What we did once of raft was in was got my blocklayer to put down soap bars on external and dividing walls.
Then I installed the sole plate myself using a laser level, slates and express nails.
Your soap bar needs to be level within +-3mm.

Talk to your engineer about this lad.

slowharry

thanks all

my thinking was rather than excavating strips, pouring strips , laying rising walls, stoning up and laying a subfloor. the man i have lined up to do earthworks has a steel fixer and can fix the raft and he can pour it. this would have all been done with proper drawings rather than what someone thinks they remember was done on the last job they were on.
as i've said the raft option was purely down to choice as the ground conditions are as good as you can get where i am. i wasn't 100% sold on this and was playing devils advocate myself with the details.

thanks again

sprinkles

You'll need to excavate the top 400mm in any case - the strips aren't all that much deeper (provided the ground isn't sh*t). The amount of labour intensive steel fixing req for a raft makes strips a no brainer for me. It might look easier on paper but believe me - if he's planning on doing a proper job it'll be easier/cheaper to go with strips.

Rafts are only economic in poor ground conditions were strips might need a meter or 2 of lean mix below them.

Anyway, best of luck with it.