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Foundations & Footings 101

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Avoiding Common Self-Build Issues

30% Underground

Writing for Build-It’s Self-Build Zone. Andy Butcher reminds us that one of the most important parts of a project is to ensure you’re dealing with well-designed, properly-realised foundations. Considering 30% of build costs will be underground, there is a lot to think about. “What’s more” he adds, “the work will need to be thoroughly mapped out well before you can get underway.”

Gathering information

  • Troubleshooting the crucial foundations phase can lead to you enjoying a successful home building project. A suitably-qualified professional such as an architect, engineer or surveyor would normally design the foundations “Don’t just rely on your builder” says Butcher, but this is good advice for builders as well.. A number of factors must be considered, so it’s worth investing time and money at this stage.

    • False Economy

  • Butcher strongly recommends having a soil survey on your site. This is often forgotten about or rejected as an unnecessary expense – but in my experience, this is not only a false economy but could lead to major issues later on. There’s a common phrase in the construction world that we all need to remember: “money is either made or lost in the ground.”

    • Investigations

  • Guided by your building professional, the examination could either use prior knowledge of the local area, take the form of a simple desktop study, or be based on specific site information. If none of these are available or there are other influences at play, a formal site investigation should be carried out to confirm the nature of the subsoil(s).

    • What & Who Else is Involved?

  • Depending on location, you may need to commission reports into evidence of radon, contamination or previous mining activity. In some instances, you might require arboricultural advice, especially if there are Tree Preservation Orders (TPOs) in place or specimens nearby on land owned by other parties.

    • Water

  • The presence of groundwater should also be factored in. This can affect the foundation type and waterproofing – especially if you’re adding a basement, as there will be extra Building Regs and Building Standards requirements to meet. To enable construction, it may be possible to ‘dewater’ locally, for instance by pumping it away during the works.

    • Penalties

  • Legislation such as the Party Wall Act and Construction Design Management Regulations might also need to be taken into account. Failure to comply won’t just delay your build but could lead to financial penalties, fines or even a custodial sentence.

    • Designing the foundations

  • Once all the information is to hand, your team can draw up the foundation design. Generally, the aim is to use a simple, cost-effective strip or trench fill method – but there’s a traditional cut-off point of 3m deep, at which point a change in the type of foundation is likely to be considered. This is partly due to the expense of the concrete you’d need, and partly for the health and safety of personnel working at depth.

    • Piles

  • Beyond 3m, piles or a reinforced concrete slab are likely to be the most viable options. There are many types of piling, but the most common are displacement and augured piles – both of which would be planned by a specialist contractor.

    • Trees

  • If trees are present, the design must accommodate them. In a cohesive (clay) soil, foundations may need to go deeper because of the possible presence of root systems – and should comply with Table 4.2 Building Near Trees in the NHBC Guide. Removing specimens close to your proposed building shortly before construction can lead to heave (water released causes clay soil to expand), which could lead to long-term damage to any nearby houses.

    • Going on site

  • The design will need to be approved by the relevant building control body via a plan check. They will then visit the site for a final sign-off. I’d recommend the in-situ foundations are also reviewed and signed off by your chosen building professional (eg the house designer).

    • Groundworks & Claims

  • Use a competent groundworker who is adequately insured with an A-rated insurer. There could be hidden dangers underground such as utility cables, pipes and sewers that might need redirecting. Damage caused to these can lead to multi-million pound claims – so always insist on seeing proof of the contractor’s insurance or a letter from their broker/insurer.

    • Beware the Unexpected

  • No matter how much you plan, it’s still possible to find unexpected issues – particularly close to other buildings or on brownfield plots. So it’s important to set aside a decent contingency in your budget.

    • Greenfields

  • On undeveloped greenfield sites, little will be known about conditions below ground. Traditionally you’d commission a small trial hole to confirm the soil type, combined with a percolation test to enable any soak away design to be carried out. If possible, your designer and building control inspector should be in attendance to agree a way forward.

    • Last Minute Work

    • With trench fill, your inspector and warranty provider will normally want to approve the excavations prior to the concrete pour. The trenches should be cleaned out, with the sides true and square, and any water that’s seeped in removed. So be prepared to do some last minute work – and bear in mind that you may be asked to dig a little deeper if soil conditions aren’t quite as expected.

    Andy Butchers is a building surveyor with over 25 years’ experience in the construction industry. He is a Director of Build-Zone Survey Services. He regularly shares his knowledge to help self builders and renovators avoid and overcome issues with their projects. You can read more expert advice from Andy by visiting Build It’s Self-Build Zone directory page.

    Foundations for Timber Frame can be Simpler & Cheaper

    Consider this. A typical 2 storey 150m2 house will weight around:
                                                               Brick & Block superstructure = 80 MT
    Timber frame + brick skin = 48 MT
    Timber frame + timber cladding  = 15 MT  

                                          (see How Much Does the Timber Frame for a House Weigh?)

    So at around 1/5th the weight of an all-masonry superstructure, a timber frame will need less money spending on foundations – whatever the ground conditions. And that translates into easier designs, faster builds, lower costs, higher profits and/or lower house prices.

    DfMA to the fore!

    To realise these benefits does, of course, need the architectural designer to understand not just that Timber Frame is lighter, but the way in which such buildings work as a structure. In turn this requires an appreciation of the way they are manufactured. Transported and assembled on-site.  All of this entails a shift in thinking to what is now increasingly referred to as DfMA - Design for Manufacture & Assembly.  This is already available via established ‘Off-Site’ manufacturers and is quickly and easily incorporated into procedures and processes of building and development. Better still, you can make partnering arrangements with such manufacturers to gain all round benefits.

    Technologically ‘SMART’ Homes

    As Off-Site Construction matures into DfMA it is clearly at the forefront in turning construction workers into technical deliverer and enablers for such delivery. At the same time it is exceptionally well placed  to incorporate rapidly increasing demand from buyers for their new homes to be ‘Smart’, e.g. by the incorporation of energy saving and TIoT (the internet of things) to deliver major components.

    Greater Speed, Accuracy, Quality and Lower Costs via Collaborative Partnering

    Greater collaborative ‘partnering’ between architects, builders and  manufacturers will accomplish this The greater speed, accuracy and quality that can result from manufacturing components in a dry, controlled factory environment, together with the ability tom incorporate (yet to be invented) ‘Smart Ware’  gives home builders perhaps the only way of achieving this, together with improved on-site build quality AND controlling costs.

    Resistance Disappearing

    While resistance to the change to DfMA has been the norm, the wish of most UK Builders to deliver excellent customer service and top notch homes is now driving an increasing number to choose Off-Site for their developments. Also, as ‘OffSite Hub” note, architects and designers are moving toward DfMA, something w have been encouraging for over 20 years. The emergence of LA Developers will only speed up this process.

    Easy Timber Frame

    To assist them in doing so our “Easy Timber Frame “ now offers standard size modular timber frame elements for them to use as a design base, cutting down on technical design and engineering to produce win-win results.

    Better all-round Savings

  • Our specialist services and CUSTOM homes division deliver best value and  protect the interests of land owners, house-builder developers, professionals and private individuals seeking to build their dream home. Our off-site construction systems also reduce the amount of material that gets wasted on site, helping to avoid land fill, hazardous waste separation and handling, They also deliver better value for you and your customers.

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