# Concrete Block, brickwork & lintel specification for house & garage?



## Corner (27 Jan 2010)

What is the recommended specification for blockwork on a dwelling? E.g. what strength should be specified for:

(a) internal walls, 
(b) external walls and 
(c) dead-building/footings? 

To give an idea of the contruction of my walls from inside to outside, typically I have 215mm inner leaf (block on flat), 100mm cavity, 100mm outer leaf and 200mm natural stone cladding. The 215mm on the inner wall is required to take structural load of pre-cast hollow core slabs. 

Also, is there a recommended specification for: 

(a) red bricking and
(b) lintels (which will need to take the weight of the natural stone cladding also!)

Thanks!
Corner.


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## DBK100 (28 Jan 2010)

Corner,
There is ample information out there on self-build sites / forums / and manufacturer's websites.
More than likely you will get answers from people here pointing you towards particular block strengths, specs for wall ties and lintels etc. and referring to various 'rules of thumb'.

A critical point to remember is that no one who gives you information here can or will be standing over their advice. If defects were to arise at a later date it will be you alone who will have to accept liability.
In the normal course of events, if an engineer friend gave you advice which directly resulted in defects, you would have cause for action even if you had not formally engaged them. He would still be expected to provide the level of expertise and competence he has attested to. 
On a web forum you are seeking advice from a person unknown to you.

The best thing you can do for your own protection & peace of mind is to engage a competent person to advise you on such matters and therefore have a direct contractual relationship with them. This protects both parties in the event of problems.
Or,
If you are comfortable, gather the information yourself from sources mentioned above or suitable technical books ( http://www.amazon.co.uk/Mitchells-Introduction-Building/dp/0582473039 ).

Personally, (and bearing in mind that I am an architect) I would not take the advice of even a friend who was an engineer, surveyor, solicitor etc., unless I had engaged them and paid them for their work. By engaging them you are getting the benefit of Professional Indemnity insurance as well as expertise. The last thing I would want is to find myself in a situation where their advice has resulted in my loss and I don't have any comeback.

DBK100 - MESH Architects


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## onq (28 Jan 2010)

Hi Corner,

+1 what DBK100 has advised you and I'll add this.

Focussing like this on single issues is not how best to build any building. It may be how some self-builders do it, but its not how professionals do it, and I can only draw on my professional experience. When advising you here, remote from the situation and in the presence of unknowns, we are talking principles, not specifics.

To specify a heavy duty construction like this [and I have designed three houses built using similar construction in Dublin] you need an engineer working with your architect. Its the engineers job to specify the structure, and the architect's job to make sure it doesn't adversely impinge on the design. They work together to address any conflicts, avoid unsightly projections, relocate support walls, install beams, avoid cold bridges and so on. They work together with your contractor improve buildability and reduce cost. They also consider, assess and highlight any special risks to the contractor to comply with Health and Safety regulations.

If you have no professionals on board, the role of the designer at construction stage resolving all these problems rest with you. If you don't resolve them and you're a self builder without a main contractor, all the resulting problems are your responsibility including discharging the contractor's duties under Health and Safety.

There is a balance to be struck between any design and its structural method. If the house is straightforward and designed on principles established by the building regulations, you may have a comfort zone, but an engineer should still write the specification and issue structural drawings. In my opinion a specialist or non standard design definitely requires a higher standard of professional input and should not be attempted by a self-builder without professional advice.

Do not rely solely on an engineers drawing, though. One area of confusion is sometimes the design of the stairs - people forget to take into account the depth of insulation, underfloor heating and floor covering, especially if the stairs supplier is working solely to the engineer's drawings. The stairs is often made incorrectly regarding the finished levels. Sometimes you can be lucky if you have exactly the same build up from the slab on all floors, the total rise will be okay, but the fixing points will be different to those shown on the engineers drawings and a poorly fixed stairs can fall and cause injury.

Another area of confusion is where a place restricted head height becomes even more restricted due to the plaster finish [edge of stairwell] or where there is insulation under a sloping roof soffit [balcony to bedrooms]. Some insulation systems require you to have warm-board below the roof joists to achieve the required insulation depth. Unless someone with architectural training reviews the entire design for little things like this and co-ordinates the engineers structural solution with the original design drawings with GA's at say 1:50 and key sections at 1:20 scale [say], then the developed details, which tend to focus on things at 1:10 and 1:5 may be locally correct, but you could still end up with a non-compliant house.

Finally, if you're using an architect or architectural technician or engineer, do involve yourself and ask them questions. I've recently reviewed a set of drawings which had discrepancies at planning drawing stage between elevations and plans [door missing, etc] and where a sheet of details supplied showed different cavity and insulation specifications. The owner had spotted some of them already and this level of interest is a must when you're building your own home. My best advice is to employ competent professionals, but do not put your architect or engineer on a pedestal. Don't be afraid to "put 'em undah pressuh" to perform competently, because you're paying the bill and mistakes do happen. If you're getting an amazingly cheap service, this monitoring is essential because, _inter alia_, you get what you pay for.

Similarly do not become your builders "pal" because he also has a checking function under most well-written contracts [like the RIAI forms of contract] and any disputes may well arise from the defects in the built work. Even a compliant design and a competent builder will need professional-level co-ordination to ensure quality work is done achieve your dreams on site.

I'm not taking the time to write this to talk down to you or be patronising or make you feel inadequate - I see you walking into something showing great interest but possibly not knowing where your limitations are or the kinds of legal responsibility you may be getting into. I'm writing this to bring a degree of foresight to your project to help you avoid problems going forward. The last place you need to discover your limitations is when you're in the middle of it, with deliveries due, non-compliant work to demolish and mounting bills to pay. If this post helps other self-builders avoid pitfalls that's all I can ask for.

HTH

FWIW

ONQ.

[broken link removed]


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## Corner (28 Jan 2010)

Hi ONQ,
Appreciate your detailed response (and DBK100's). Specific items such as the ones I've raised in this thread are merely queries and thoughts that sprung to mind and are purely for my own knowledge and learning and out of interest. I will not be attempting to specify the materials for my house. My dwelling has been designed by a professional (architect) and I will be retaining professional services for the construction stage. I'll have enough to do and won't be trying to do their job as well! But I do think it's beneficial to cross check & query parts of my design even if the items raised are specific. As you say, you must have the interest and involve yourself. If nothing else, it keeps people on their toes. I couldn't agree more with this approach which has proved invaluable to me to date. The extra time & thought spent before the project goes to site costs nothing but if matters are not thought out, it'll cost me down the line! 

Corner.


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## onq (28 Jan 2010)

One bugbear you might keep in mind that has reared its head during the recent cold spell is the environment of attic spaces. I'm forming the opinion that attics should be vapour checked, ventilated and insulated with materials laid along the line of the sloping roof from the get go to avoid the kind of condensation problems we've been hearing about.

This will avoid the unworkable detail of trying to seal around downlighters and as well as avoiding risk from covered up services and pipes that follow on from 300mm quilt installations as well as the blocked eaves vents. It leaves the attic ready to be floored out and converted. It will add cost during the build however.

The main benefit for householders and insurance companies alike will be a reduced risk from burst pipes burst pipes in cold weather. The plumbers January windfall may never be the same again. 

ONQ.

[broken link removed]


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