Pros and Con's of concrete beams

Dunedin

hi there, not sure if I'm on the correct page here but please feel free to re-direct me if necessary.

Just about to start building my house - story and half dormer.

can someone in the know re concrete beams advise if they are worth the extra cost versus timber joicing.

what I like about them is the solid structure upstairs versus (sometimes) creaky floors.

The foundation of the site is good i.e. very solid ground so no issue in carrying the extra weight.

all responses appreciated.

KingMambo26

It's not just the addition of a concrete beam here and there you have to think about, as the whole structure of the house is going to change. Those beams have to be supported by proper pillars instead of using the traditional load bearing walls. This also means, if properly designed, that you can get rid of internal walls in favour of open spaces as the beams will take the load of the level above.

Concrete rules!

Lurching

I presume by concrete beams you mean a full concrete slab upstairs?

If so, its definitely worth the money.

Sound is the major factor for me.

Dunedin

KingMambo26 wrote: »

It's not just the addition of a concrete beam here and there you have to think about, as the whole structure of the house is going to change. Those beams have to be supported by proper pillars instead of using the traditional load bearing walls. This also means, if properly designed, that you can get rid of internal walls in favour of open spaces as the beams will take the load of the level above.

Concrete rules!

I would have thought that this woudl be dependant on the length of the spans from Wall to Wall internally.

Equally, would internal walls built with 4'' blocks on the flat not be sufficient to carry the beams??

please feel free to disagree or othewise as this is only own view.

Dunedin

Lurching wrote: »

I presume by concrete beams you mean a full concrete slab upstairs?

If so, its definitely worth the money.

Sound is the major factor for me.

yes is the answer.

Do you have any idea of what the extra cost might be

Supertech

Dunedin wrote: »

hi there, not sure if I'm on the correct page here but please feel free to re-direct me if necessary.

Just about to start building my house - story and half dormer.

can someone in the know re concrete beams advise if they are worth the extra cost versus timber joicing.

what I like about them is the solid structure upstairs versus (sometimes) creaky floors.

The foundation of the site is good i.e. very solid ground so no issue in carrying the extra weight.

all responses appreciated.

Cons (or issues to watch out for) - Aswell as the structural implications (additional beams, possible additional blockwork, additional foundation costs) you'll also need to consider how you run and conceal services along the soffit of the slabs (electrics, plumbing); wastes which might normally run in between joists have to be routed above the floor level; vertical routing of services need careful consideration to avoid costly coring of slabs; airtightness detailing; possible additional costs for structural design; junction between floor slabs and stairs needs consideration; you'll also have the additional cost of crane hire unless you decide to go for a cast in-situ slab.

Pros - better sound performance; screed upstairs allows option of underfloor heating; also allows option of solid partitions upstairs;

Dunedin

Supertech wrote: »

Cons (or issues to watch out for) - Aswell as the structural implications (additional beams, possible additional blockwork, additional foundation costs) you'll also need to consider how you run and conceal services along the soffit of the slabs (electrics, plumbing); wastes which might normally run in between joists have to be routed above the floor level; vertical routing of services need careful consideration to avoid costly coring of slabs; airtightness detailing; possible additional costs for structural design; junction between floor slabs and stairs needs consideration; you'll also have the additional cost of crane hire unless you decide to go for a cast in-situ slab.

Pros - better sound performance; screed upstairs allows option of underfloor heating; also allows option of solid partitions upstairs;

cheers for the detailed response.

what depth of foundation would you recommend in allowing for the extra weight of the beams. As said earlier, the ground is a very hard type soil.

Supertech

Not my area of expertise I'm afraid Dunedin - each site will have different conditions, and will require specific design based on soil type and loads. Talk to a local engineer about the overall structure of the house.

KingMambo26

Dunedin wrote: »

I would have thought that this woudl be dependant on the length of the spans from Wall to Wall internally.

Equally, would internal walls built with 4'' blocks on the flat not be sufficient to carry the beams??

please feel free to disagree or othewise as this is only own view.

Without knowing the particulars of the house design I would say yes, the internal span definitely plays a role and if it is too small you may end up with a situation like killing a sardine with a torpedo. As other posters have mentioned there are ramifications affecting joisting (you could avoid some of this problem if your cabling is done on the walls rather than on the beams or pillars), foundations (these may require changes to the design of the foundation and additional cost).

Depending on the material you choose for your upstairs floors (i.e concrete slabs, wood, hybrid) you will have to modify the design of your beams.

In short, you definitely need to talk to a qualified engineer and get him to look at your plans.

dan_d

OP, a concrete slab (depending on the thickness) will have to be supported, usually by columns. Depending on weights etc, columns are usually arranged in grids, with the max distance between the columns being about 7m (give or take). I don't know how big your house is, or how your downstairs is arranged, but will you have the space to have columns every 7m (ish - very approx) on a grid running from front to back of house, and side to side?

One way to possibly avoid this would be to support your slab on the external walls of your house, and with strategic columns/concrete walls internally on the downstairs of your house. Again, I don't know the details of the house, so can't advise you there (and I wouldn't over the internet anyway). You might know if that would work for you.Another option would be drop beams cast into your first floor slab - you lose ceiling height that way.

Thirdly, you will either have to cast openings where necessary for services to travel up from the ground floor, or else core holes (extreme case), for where you want pipes/electrics. Costly.

Finally, I am getting the impression that you are not involving an engineer in this....you will have to have an engineer to design the slab and reinforcement, supports, and foundations, because otherwise....well, it won't be pretty!!In short, concrete is possible, but go and employ a structural engineer if that's the road you're taking.

sprinkles

For a typical house, with spans of about 5m between load bearing walls, then the walls should be able to carry the load. You may need large lintels/steel beams over larger openings in the load bearing walls - for instance if you have a sliding patio door to the rear - this would need to be designed by an engineer. Do you have any plans of the house? I'd be happy to take a look and give you a few sizes of what you'll need for costing purposes.

Hollowcore concrete slabs are relatively cheap and very fast to install. It'll all depend on what your builder has worked with in the past. There's a lot of options out that - something like beam and plank, which comprises of precast concrete beams with infill concrete blocks. Longer to install but requires less crane-age, if any.

Here's a link to a few suppliers/manufacturers that I have dealt with in the past.
Concast
Creagh
Whelans

Supertech pretty much hit the nail on the head with the pros/cons. You'll need a false ceiling to conceal the services. You could run the services in the screed above and drop down but that really restricts any future changes to the layout of lights etc.

Dunphus

I'd say go with timber. Sustainability ftw. I don't see the justification in concrete for small residential buildings personally

sprinkles

Dunphus wrote: »

I'd say go with timber. Sustainability ftw. I don't see the justification in concrete for small residential buildings personally

Concrete can be very eco friendly, even for small buildings. Especially if you maximise the use of GGBS in the mix design, more info here. Also every part of a concrete slab can be recycled. Sustainability in construction is a far reaching concept, you must look at not just the sourcing of the material but also the amount of carbon used to manufacture, transport, erect, maintain and demolish the structure as a whole.

Dunphus

sprinkles wrote: »

Concrete can be very eco friendly, even for small buildings. Especially if you maximise the use of GGBS in the mix design, more info here. Also every part of a concrete slab can be recycled. Sustainability in construction is a far reaching concept, you must look at not just the sourcing of the material but also the amount of carbon used to manufacture, transport, erect, maintain and demolish the structure as a whole.

I know I know but concrete doesn't grow on trees. GGBS, pfa, recycled aggregates etc. aren't the same I don't think. That is provided your timber was shipped from scandinavia by concorde with one quick spin around the world for good measure. I just like a good wood and brick house!

sprinkles

GGBS can actually render you negative in terms of carbon offset as it's a waste product of the steel production process. Everything else is locally sourced. Timber, incl shipping and heat treatment etc can prove just as bad in terms of embodied energy. I looked at this in depth on a number of fairly large projects in Ireland over the past 3 -4 years and concrete was always in the running as most sustainable product.

I'm not saying that timber isn't more sustainable than concrete in this instance but I don't think concrete should be chalked off for that reason.

Anyway, OP my offer is there if you want me to give you rough sizes for costing, just need a sketch with dimensions of what you plan on doing. PM me.

Dunedin

I have since being talking to other people on this and another suggestion woudl be to pour a slab of contrete (think 75mm) direct onto the joisting.

This involves having the joisting closer together, ply sheeting on top, heavy duty polythene over and then pouring the floor.

it's about €2 cheaper than the hollowcore and by all accounts, it seems a good job.

any thoughts on this.

Supertech

Personally I don't like the 'mix and match approach' Dunedin. I'd either go for timber or for concrete. With that construction there's a risk that the timbers may be damaged by the wet screed, and I'd reckon the additional load imposed by the screed might also increase the section size of the timber joists aswell as reducing the centres. I'd reckon that the floor will require additional propping and for a longer period of time than a traditional timber construction, meaning access is restricted underneath aswell possibly holding up other trades, so in essence you're getting the disadvatages of a concrete floor aswell as the advantages. Your joists will also need to be completely level to avoid cracking in the screed, so the cost may well balance out in the end when additional labour and material costs are factored in.

Depending on the floor area your talking about €2 is not a huge amount (presumably per sq.metre) over the lifetime of the house so I'd go for the hollowcore in that instance every time.

Have you considered using a timber floor structure and soundproofing that using resilient foam slips under the floor deck and maybe double plasterboard in the ceiling. There are soundproofing details out there which apply to timber structures which may work.

Dunedin

Dunedin wrote: »

about €2 cheaper than the hollowcore and by all accounts, it seems a good job.

.

sorry meant to say €2,000 cheaper than hollowcore in the over all job.

(floorspace is circa 1330 square foot)

F00t13f4n

We've just finished building my dad's new house, and were considering putting in either reinforced concrete or hollowcore floors. We used 150mm thick concrete walls downstairs, so the concrete suspended floor seemed like a logical idea too. One of the main reasons for looking at concrete was to reduce the noise transmission through the floor.

In the end we went with timber. We have floorboards screwed to the joists rather than nailed, so they shouldn't creak. We put plywood over this and 2 layers of plasterboard for the ceiling.

Make sure you consider all the issues with forming a concrete upper floor. You will be getting another trade on site later in the job, so there may be access issues. You'll need to get the wet concrete to the higher level, which will probably need a pump. You'll have to set out conduits or sleeves for telephone lines, water pipes, electric cables, etc prior to casting the floor. Changing your mind on any of these will take a lot more work than drilling through floorboards. You'll probably have to prop under the wet slab, so won't be able to do anything else in the house until it reaches sufficient strength.

I would put in a timber floor and put in extra sound dampening, but good luck with whatever you choose to do!

FesterBeatty

Dunedin wrote: »

I have since being talking to other people on this and another suggestion woudl be to pour a slab of contrete (think 75mm) direct onto the joisting.

This involves having the joisting closer together, ply sheeting on top, heavy duty polythene over and then pouring the floor.

it's about €2 cheaper than the hollowcore and by all accounts, it seems a good job.

any thoughts on this.

...differential expansion between timber & concrete will leave you with cracking problems throughout, its just a terrible detail. Nevermind the fact that your joists will be quite deep and/or closely spaced.

It was also noted that the floor may require propping for longer...? Why would anyone prop a timber floor at all? The addition of a concrete topping has no structural benefit whatsoever (i.e there is no composite action to be gained) so if the joists cannot cater for the weight of wet concrete in the temporary or construction phase, then they naturally cannot cater for the permanent loads.

If it was my house I'd go with wideslab precast floor. But of course, you need a structural engineer to design all structural elements including foundations - naturally you cant expect any engineer to size/specify foundations via an internet forum..