Arch tech supervising when structural raft required

sas

Hi,

I will be using a structural raft for my house. This is because I am planning on building a passive house and will be used an insulated raft.

I would like to use the architectural firm that designed the house for the supervision of the build.

However, they cannot certify a structural raft and hence an engineer would be required also for this part.

This presumably means there is dual responsibilty. In the unfortunate event that an issue arose, I could find myself in a situation where both parties are blaming each other. Obviously this would add to what would already be a very stressful situation.

Am I correct in this assumption of dual responsibility?

I presume that alot of people will have opinions on this as I can only imagine it's very relevant to some of you.

I'd simply use an engineer for the whole job but I'm struggling to find one that is interested in what I'm trying to achieve, even in the current climate.

The architectural firm I used have been very supportive and interested for the whole process. I know I can work with them.

Supertech

There's no dual responsibility. The raft foundation is a specialist deisgn and a structural engineer is therfore required. If there's a problem with the raft later then it's the engineer's responsibility. Engineer designs the raft as a consultant to the AT, and gives the relevant guarantees associated with this work.

Specialist structural design is not within the remit of your Architecttural Technologist and he / she would be unwise to undertake it, as indeed you would be to allow them to.

muffler

Supertech wrote: »

There's no dual responsibility. The raft foundation is a specialist deisgn and a structural engineer is therfore required. If there's a problem with the raft later then it's the engineer's responsibility. Engineer designs the raft as a consultant to the AT, and gives the relevant guarantees associated with this work.

Specialist structural design is not within the remit of your Architecttural Technologist and he / she would be unwise to undertake it, as indeed you would be to allow them to.

+1

sinnerboy

SAS it is the norm for an architectural practice to work with a structural engineering practice with dual supervisions and certifications issuing .

In the case a very big ( 8000 ft2) house we did about 3 years back - there was a building services engineer appointed also - with M+E supervisions and certifications issuing

sas

Supertech wrote: »

There's no dual responsibility

I may not have made myself clear. I didn't suggest allowing the arch to design the raft, nor would he even suggest it.

Lets assume that cracks start to appear in the walls upstairs only. This may be impossible but I'm speaking hypothetically. Bad cracks can be a sign of subsidience I understand. BUt not necessarily. So the arch firm blames foundations and engineer that certified raft blames roof that arch sign off on.
We're trapped in the middle with additional stress.

These things may be easier to diagnose than I think so it may be a none issue.

This basically was the basis of my original post.

sas

Supertech wrote: »

Engineer designs the raft as a consultant to the AT, and gives the relevant guarantees associated with this work.

So would the foundation stage still be signed off by the AT?

sas

In the same vein so I'll keep going here.

When AT supervise regular more traditional houses how do they determine lintel sizes etc. if there is a hollow core first floor for example?

What I am trying to do now is determine what the role of the AT in the certification stage of my home would be.

AT was definitely the right person for planning\design in my case. Also for specification of insulation etc. And general validations that I wasn't suggesting complete madness in some cases...

However, in a project like mine where there is a structural raft, large spans over windows (is 4 m large?, more structural calcs?), and a roof space that is going to be completely open and supported by steel etc I am beginning to think that sticking with an engineer is the most practical. As long as I can find one that will appreciate what I want.

The actual insulation and detailing spec. will be done by a member of the PHI if I finally commit to going the certified passive route. I have an offer from them that I am considering at the moment.

What am I missing that an AT would add at this stage based on the limited info. I've provided for my project? Have I answered my own question?

All advice is hugely appreciated.

sinnerboy

sas wrote: »

So would the foundation stage still be signed off by the AT?

Yes . You will have one person responsible for payment certs . AT will take advice from SE when issuing that cert for payment . They work in consultation

sinnerboy

sas wrote: »

In the same vein so I'll keep going here.

When AT supervise regular more traditional houses how do they determine lintel sizes etc. if there is a hollow core first floor for example?

What I am trying to do now is determine what the role of the AT in the certification stage of my home would be.

AT was definitely the right person for planning\design in my case. Also for specification of insulation etc. And general validations that I wasn't suggesting complete madness in some cases...

However, in a project like mine where there is a structural raft, large spans over windows (is 4 m large?, more structural calcs?), and a roof space that is going to be completely open and supported by steel etc I am beginning to think that sticking with an engineer is the most practical. As long as I can find one that will appreciate what I want.

The actual insulation and detailing spec. will be done by a member of the PHI if I finally commit to going the certified passive route. I have an offer from them that I am considering at the moment.

What am I missing that an AT would add at this stage based on the limited info. I've provided for my project? Have I answered my own question?

All advice is hugely appreciated.

SAS - the AT should remain as your lead consultant . The SE will work with him together as a team during the detailed design process . I work with some fine engineers - and I do not dis service them when I say they will freely admit that the best finished product is arrived at by this team work .

The very best engineer I know - I guy in his 50's a really good guy - has said often that he would not dream of designing - and crucially - going through the build process himself if he was working on his own house

In the case of simpler projects where lintol spans are small and there are realy no challenging structural aspects to the build - the Homebond manual is full of span tables for joists , rafters , lintols etc - in this case an SE is not required above foundations

Poor Uncle Tom

sas wrote: »

........What I am trying to do now is determine what the role of the AT in the certification stage of my home would be.

AT was definitely the right person for planning\design in my case. Also for specification of insulation etc...

In your case the role of the AT would be to certify stage completions for bank/financial purposes. The AT will not sign off until he/she have the necessary reports/certs from the others, eg., raft cert from SE, commissioning report for the treatment system, RECI/similar cert for ESB, etc.

The AT's role is to make sure the jig-saw comes together properly, not to make the parts for the jig-saw.

sas wrote: »

However, in a project like mine where there is a structural raft, large spans over windows (is 4 m large?, more structural calcs?), and a roof space that is going to be completely open and supported by steel etc I am beginning to think that sticking with an engineer is the most practical. As long as I can find one that will appreciate what I want.

Most of the above are specific jobs for a SE and your job will need one.

Who you award the job of project certification and final compliance certification to is a matter of who you figure you will get the better job from. Personally I think the people who designed the house are the best to know how it goes together.

A Certificate of Compliance from the person/people who designed your house at the end is validation that you have a complete package finished to the satisfaction of the person who first conseptualised it. I think that's worth the extra couple of thousand in the overall project, especially as you do seem to rate them.