Foundations with Ringbeam??

curaldo

Hi,

I was just wondering what the consensus was on foundations using a Ringbeam to support a timberframe construction.

Looking into how different the process is to standard foundations kind of scares me. It seems that you pull off the top soil, put down some compacted hardcore, then your insulated ringbeam mould is put down, then three layers of insulation split with radon barrier between second and third. Rebars goes into the ringbeam. Then you pour your concrete floor and ringbeam. A bit simplified but you get the gist. The ringbeam construction is suppose to stop cold bridging. It seems alot less hassel and looks cheaper.

Whats the standard way of doing your foundations for a timberframe. Do you just dig and pour the external walls. Build your footings, hard core, insulation, mesh etc?

Im asking this questions because im going to build in the next few months and i want to do it right, as we all do. I want to build a well insulated, breathable, energy efficient timberframe. Only a few companys out there have breathable walls. The majority don't, Why? Am i missing something. Thanks.

justflow1983

I'm not really familiar with using a ringbeam. Timber frame can be put up onto a block rising wall if you want, but like you noted you get a thermal bridge at the bottom corner.

Two other ways to get around the rising wall are to use an internally insulated basement (common in the US) or to have a post foundation with the building suspended above ground (common on the continent). In the second case, the joists are not touching the ground and you insulate between and below them.

I've found that any timber frame company will build TF any way you like as long as you have a good set of details and are willing to stick to your guns. A lot of them don't do breathable construction as standard because they either don't want to pay for the materials or they just don't know any better.

curaldo

Thanks justflow,

Do you know were i can get more info on post foundations and have you heard of anyone using them?

sydthebeat

curaldo wrote: »

Hi,

I was just wondering what the consensus was on foundations using a Ringbeam to support a timberframe construction.

Looking into how different the process is to standard foundations kind of scares me. It seems that you pull off the top soil, put down some compacted hardcore, then your insulated ringbeam mould is put down, then three layers of insulation split with radon barrier between second and third. Rebars goes into the ringbeam. Then you pour your concrete floor and ringbeam. A bit simplified but you get the gist. The ringbeam construction is suppose to stop cold bridging. It seems alot less hassel and looks cheaper.

Whats the standard way of doing your foundations for a timberframe. Do you just dig and pour the external walls. Build your footings, hard core, insulation, mesh etc?

Im asking this questions because im going to build in the next few months and i want to do it right, as we all do. I want to build a well insulated, breathable, energy efficient timberframe. Only a few companys out there have breathable walls. The majority don't, Why? Am i missing something. Thanks.

it sounds like you are describing 'insulated raft foundations'.
eg http://www.isoquick.de/en/bauverlauf.html

i have seen this installed and i am impressed. It does add approx 10K to your build costs.

a few points, assuming ive taken you up correctly.

1. theres no ringbeam, the whole raft is reinforced. the whole raft sits on a bed of high performance dense polystyrene insulation

2. dont know what scares you. this is a technological advancement required (pretty much) in the construction of passive houses. Its a proven technique.

3. it suits EWI builds, single skin timber frames, and even icf if properly designed.


if you are using if for a timber frame build, you wont have a block outleaf. You are looking at specifying a cladding of cement board such as aquapanel. there are typical passive level details for this construction in this book...

http://www.amazon.com/Passivhaus-Bauteilkatalog-Details-Passive-Houses-Konstruktionen/dp/3211297634

justflow1983

curaldo wrote: »

Thanks justflow,

Do you know were i can get more info on post foundations and have you heard of anyone using them?

I can't think of any off hand. I do know that they're used in scandanavia and germany, so it shouldn't be too hard to find more info. There may be dampness issues or other problems that keep it from being done in ireland, I'm not sure.

Its basically a treated timber or concrete post coming out of a footing. Then the building sits on that, you do a suspended joist floor just like you would internally in a timber building, but the difference is that on the exterior you add a layer of insulation and then something inert like concrete fibreboard or something. I've never done it but seen it many times in alpine places. I would assume the rising post is separated from the rest of the building by a dpm. Its a very green way to do it in that it greatly reduces soil disturbance as well as the amount of concrete going into your building.

In addition to Syd's suggestion of the Aquapanel, if you are rendering onto timber clad you can also render onto Sto glass fibre render backers. I've also seen lime render put onto heraklith, which is a wood fibre material if you want to go the natural route.

Syd, good call on the raft foundation. I ought to learn more about that one myself.

sydthebeat

justflow1983 wrote: »

I can't think of any off hand. I do know that they're used in scandanavia and germany, so it shouldn't be too hard to find more info. There may be dampness issues or other problems that keep it from being done in ireland, I'm not sure.

Its basically a treated timber or concrete post coming out of a footing. Then the building sits on that, you do a suspended joist floor just like you would internally in a timber building, but the difference is that on the exterior you add a layer of insulation and then something inert like concrete fibreboard or something. I've never done it but seen it many times in alpine places. I would assume the rising post is separated from the rest of the building by a dpm. Its a very green way to do it in that it greatly reduces soil disturbance as well as the amount of concrete going into your building.

In addition to Syd's suggestion of the Aquapanel, if you are rendering onto timber clad you can also render onto Sto glass fibre render backers. I've also seen lime render put onto heraklith, which is a wood fibre material if you want to go the natural route.

Syd, good call on the raft foundation. I ought to learn more about that one myself.

if your even around the abbeyleix area on mon-wed i could show you a site where its used (if sas is ok with that?)

sas

sydthebeat wrote: »

if your even around the abbeyleix area on mon-wed i could show you a site where its used (if sas is ok with that?)

Yeah, no problem. Anyone here that is interested should feel free to drop me a pm and come have a look.

I reckon the OP is describing Supergrund.

curaldo

Yep i was describing supergrund. I was also told that it could cost me around forty grand to put it in. Seems crazy expansive. Maybe i picked up the guy wrong. The one i was refering to uses 300mm of EPS. The process looks very straight forward. Something i could probably do myself with a little help. I found a company in Antrim that sell EPS but haven't been able to get in touch with them yet. Anyone know how much a sq ft this stuff costs. Thanks again for all the info.

justflow1983

Here's a close-up of a post foundation from a quick google search:
http://www.ski-epic.com/2008_papua_new_guinea/p231b_goroka_our_house_stilts.jpg

These are really common in flood-prone areas in North America as well as the alpine areas in Europe that I previously mentioned.

One more for good measure in the Maldives
http://travelregistry.co.za/wp-content/gallery/maldives/maldives_house_on_stilts.jpg

beyondpassive

You can buy the EPS yourself from quinn or aeroboard cut to size, this is the Viking-House design that I ask structural engineers to specify. It works out cheaper than strip foundation, uses less concrete and is simple to assemble, most self builders put the formwork together themselves. I generally specify it because the Radon barrier detail is simplified.

DSC00601.JPG

For rain screen an alternative to Aquapanel is renderpro, it's much cheaper and not as robust. You can also put a block outer leaf outside the EPS raft, but it has to be calculated to take accound of soil conditions and the locations of point and distributed loadings.

beyondpassive

Just found the specification for those interested in the science behind EPS foundations. I'm not supporting one system over another, all have their merits, Lars Petterson has had great success with his system, Supergrund have done some great work in Clockjordan and I've heard Isoquick's professionalism and attention to detail is beyond compare. But its a case of different horses for different courses.

Two things to beware of,
one, we usually visually have a recessed plinth, in Scandinavia they often have a bullnose plinth. It can look wrong if it is not considered.
two, you have to be careful that the concrete doesn't blow out the eps formwork when it is being poured + levelled.

sydthebeat

beyondpassive wrote: »

You can buy the EPS yourself from quinn or aeroboard cut to size, this is the Viking-House design that I ask structural engineers to specify. It works out cheaper than strip foundation, uses less concrete and is simple to assemble, most self builders put the formwork together themselves. I generally specify it because the Radon barrier detail is simplified.

DSC00601.JPG

For rain screen an alternative to Aquapanel is renderpro, it's much cheaper and not as robust. You can also put a block outer leaf outside the EPS raft, but it has to be calculated to take accound of soil conditions and the locations of point and distributed loadings.

thanks for that BP.... a few queries

1. what consideration is made for internal loadbearing blockwork? is the raft deepened in these areas? is the inner L form compromised in these areas?
2. what kind of costs are you looking at for say 100 sq m basic rectangular shape? if done by self, is there warranty implications?
4. is the 100mm floor as shown in fig1 considered a sub floor, or is it used as a finished floor? can it be increased to 150mm?

beyondpassive

sydthebeat wrote: »

thanks for that BP.... a few queries
Hey Syd.

1. what consideration is made for internal loadbearing blockwork? is the raft deepened in these areas? is the inner L form compromised in these areas?
2. what kind of costs are you looking at for say 100 sq m basic rectangular shape? if done by self, is there warranty implications?
4. is the 100mm floor as shown in fig1 considered a sub floor, or is it used as a finished floor? can it be increased to 150mm?

1. ya, raft is 200 mm deep in a 300 wide strip for the load bearing spine walls, cross walls can just be built on the slab.
2a. €33 per square meter, add Vat, what 21.5% is it and its about 4k supply. When you add labour, hardcore/gravel land-drain, reo, radon, 35N concrete, underfloor pipes. It would up to cost €12k or €13k after tax to have a floor slab and ringbeam ready to accept timber frame.
2b. The loading and compression/deflection of the EPS is easily calculated, your structural engineer can work out the deflection of the EPS. The EPS 300 is quite stiff and will compress between 1+3%. This is less than subsoil or hardcore settlement. So similar to design of rafts or strip foundations, the structural engineer needs to asssess this solution for your individual loading s and soil/ bedrock conditions.
3. It's a finish floor, but with setdowns for timber floor on battens you would have 150mm floor in places. In some circumstances the EPS formwork has been placed on a concrete structural raft where ground conditions do not support universal settlement.

curaldo

Hi Beyondpassive,

how do you stop the eps from bulging when you pour the concrete? and what is a recessed plinth and bullnose plinth?

If i was to go down this route would i have to get an engineer to calculate the width of the ringbeam or is it a case of just making sure the timberframe overhangs it by say10mm?

I was considering doing normal strip foundations then putting two blocks on the flat around the perimeter and insulating them in much the same way you described only using normal kingspan instead of eps. I know it wouldn't work as well and there is an argument about kingspan losing it u-value when wet but it would save cost and stop some of the cold bridges. Do you think this is just messin around or is there any merit to it. Thanks.

beyondpassive

Timber batten bolted through EPS at butt jointed on corners, fixed with a big washer plate on the inside face of the EPS will keep the formwork from blowing out.

You are always recommended to have a structural engineer assess and supervise any type of reinforced concrete.

Normal strip foundation is a massive cold bridge, the inner leaf sits on a cold rising wall. You should use your concrete floor as a heat sink, if you have nothing but 25mm insulation between the floor slab and the rising wall, then you are heating the outside of the house. I'd try to use EPS formwork, if i couldn't do that i'd use a quinnlite foundation block, tanked on the outside. Fact is, its very tricky to insulate with a standard rising wall, it becomes very difficult to keep the lower blocks of the inner leaf warm, and heat just pee's out.

onq

curaldo wrote: »

Hi,

I was just wondering what the consensus was on foundations using a Ringbeam to support a timberframe construction.

Looking into how different the process is to standard foundations kind of scares me. It seems that you pull off the top soil, put down some compacted hardcore, then your insulated ringbeam mould is put down, then three layers of insulation split with radon barrier between second and third. Rebars goes into the ringbeam. Then you pour your concrete floor and ringbeam. A bit simplified but you get the gist. The ringbeam construction is suppose to stop cold bridging. It seems alot less hassel and looks cheaper.

Whats the standard way of doing your foundations for a timberframe. Do you just dig and pour the external walls. Build your footings, hard core, insulation, mesh etc?

Im asking this questions because im going to build in the next few months and i want to do it right, as we all do. I want to build a well insulated, breathable, energy efficient timberframe. Only a few companys out there have breathable walls. The majority don't, Why? Am i missing something. Thanks.

You seem to be suggesting a raft foundation for a simple house plan of one storey.
This kind of foundation doesn't seem to be covered in Part A of the building regulations - in Part A all loadbearing walls are required to be suported by a strip foundation.

Loadbearing walls in a two storey house can include internal walls or loadbearing studs to support first floor joists or slabs, giving a line load to be transmitted to the ground.
Houses may also incorporate point loads where there are columns or concentrated loads for example at the ends of beams, at and around stairs opes, and at masonry chimney breasts which can occur on internal or external walls.
As long as there are no point loads or concentrated loads or line loads, a slab foundation designed by a competent structural engineer may be appropriate in the case of simple, symmetrically planned houses..

The main benefit appears to be cost, but the applicability of this kind of construction is limited to very simple or very large and complex structures, because in the mid rage, where most houses exist, the preference is for well designed strip or pad foundations, or piles in extreme cases with ground beams.

In addition, unless your engineer has properly investigated and prepared the ground beforehand and designed the foundation type appropriate to the conditions, merely installing a standard spec raft foundation with some extra rebar can be a disaster waiting to happen.
Rafts can crack due to uneven settlement due to ground conditions and can even "tip" in extreme cases, where for example the ground on one site of the house is more supportive than on the other side.
Where the raft, installed by someone on a "job" basis is a generic raft, but the house isn't evenly "balanced and centred", the raft can be eccentrically loaded which can lead to cracking or differential settlement.

This problem can be exacerbated where a raft is used as a cost-effective foundation to an extension and instead of biting the bullet and tying in the new work at foundation level with a strip similar to the existing dwelling, the raft is chosen for cost and may well end up being costly, sould the raft settle and the extension rotate around the interface with the existing house.

In addition specifying a raft now for a bungalow, without internal loadbearing walls will make it difficult to allow for the later conversion of the attic.
The floor loads will require to be supporte mid-span and that means line or point loads being transmitted through studs that are not design as loadbearing elements.
If you strengthen them or replace them with loadbearing studs or loadbearing blockwork the loads they transmit must be suported by the slab, which has not been designed for this.

So the lesson to be learnt is - build cost effectively now and fail to allow for later vertical extension and you may come to regret it.
In no case proceed to site without proper site investigation, preparation and foundation design by an engineer.

ONQ.