First Floor Joists

[handyandypandy01]

I am trying to get my head around the design of first floor joists in new houses.

I know the options when designing a first floor would be:

long lengths spanning from one end of the building to the other at 400 centers, but i can see that you cannot get normal timber spanning over 5.11m.

the second option may be using i-joists but i understand these are expensive also they have a maximum span.

the third option would be to split the load using an internal wall.

My questions are...

would the internal wall need a 1m deep foundation or can you build it off of the concrete floor?

are there other options?

Thankyou

 

[DAZB]

An internal wall designed to support the floor above would need a sufficient foundation and not just sat on a concrete floor as it is essentially carrying both ends of all the upper floor joists plus any load that is imposed on them either as the 'dead load' which is the weight of the joists themselves, plasterboard, skim,insulation and even fixings etc... and also the 'imposed load' such as furniture, bath, shower tray, wardrobes and fittings etc.. plus future loads like people. Another option may be to install an RSJ instead of a supporting wall which would use the existing house walls to take the load but structural calculations and a chat with a qualified structural engineer may be the order of the day.

 

[RonnyRaygun]

long lengths spanning from one end of the building to the other at 400 centers, but i can see that you cannot get normal timber spanning over 5.11m.

Where did you see that? You might have to search around a bit, but some builders' merchants stock timber in lengths exceeding 5.1m.
You can also close up the spacings to 300mm.
What is the clear span?

Probably easier to get a steel beam designed to break the span at mid point. Sit it on padstones on load bearing walls or piers. It can be detailed so that the beam is recessed into the ceiling so no-one will ever know it's even there. This method would also allow you to have a less deep ceiling than if joists were designed to span the full distance.

It also gives you more flexibility downstairs. More choices on where to put your walls and they can be stud partitions which can be built directly of the slab if non loadbearing.

 

[jbuk]

You can get long lengths of timber but it may have to be specially ordered, my local yards do a maximum of 5.6m which is what i've just bought to replace my kitchen/diner floor

I did look for longer lengths as I needed 7metres and there are a few places on the net but there's a surcharge for extra long timber afaik