SIPs Technical and Frequently Asked Questions

The use of SIPs now has a proven track record in the delivery of high performance, thermally efficient dwellings. Historically this was advantageous for our self-build clients that wanted to exceed regulations to drive down energy bills in their forever homes.

However, with regulations under Part L and SAP 10 becoming increasingly stringent the use of SIPs removes variables and provides a streamlined route to compliance for all.


Why do SIPs systems make this process easier for the client?

As building regulations continue to become more stringent, especially with amendments to Part L and now SAP10 as we move toward the 2025 future homes standard, the use of SIPs has huge benefits to all to ensure that compliance is achieved.

Being able to guarantee U values, provide thermal bridging details and help toward ensuring air pressure test results at early design stage allows all clients to accurately cost for the overall energy performance of their build or development.

Using back stop U values, Accredited Construction Details (ACD’s) and default Thermal Bridging (PSI) Values is no longer compliant so ensuring the overall energy performance of the build is achieving your requirements at the earliest stage is the best way to avoid further costs and delays to projects.

Can you expand on this regarding the U values, air pressure tests and thermal bridging – are your SIP panels compliant with current U Value Requirements?

All projects must achieve certain U values to comply with current regulations. This is currently 0.18 in walls and 0.11 in the roof when looking at the target fabric energy efficiency of a dwelling.Hemsec SIP | Structurally Insulated Panels | SIP Build UK

However, depending on how the project is performing overall when considering additional measures such as Solar PV, Air Source heat pumps and MVHR it may be that the roof can be delivered at 0.13. Again, early modelling of the dwelling helps to confirm this which again shows the commercial advantage to having this done.

With our SIP systems we can complete U value calculations at the earliest possible stage to ensure we are achieving the required targets. With our SIP systems we are achieving these targets with the thinnest overall construction depths possible which maximises habitable or rentable space internally for the client.

Our range of SIP panels provide options as low as 0.11 in wall applications and 0.13 in roof applications depending on a project’s external finishes. SIP Panel Range

Along with U values, what is the importance of the Air Pressure testing?

There is no point delivering fantastic U values with poor air pressure test results! SIPs systems are inherently airtight given the accuracy of design, manufacture and install so our systems will often exceed current air pressure test requirements without additional measures. Obviously follow on trades must ensure they are sealing appropriately too around any penetrations made!

A significant change to the new regulations is that all plots on multiple unit developments must be air tested – even if they are the same house type. For developers, the worry of how each dwelling will perform can be eliminated when using SIPs which again reduces variables and potential costs if additional measures are needed due failed air pressure tests.

Our SIP systems also have minimal shrinkage and settlement in comparison to standard timber frame so this ensures air pressure test results are maintained through the lifetime of the building. This combined with reduced timber content in external walls also ensures that thermal bridging is kept to a minimum.

This leads nicely onto thermal bridging – what has changed under new regulations?

thermal bridgingDefault PSI values can no longer be used as this has a negative impact on fabric energy efficiency results, often leading to failure to comply.

Our SIP systems are complete with Pre calculated PSI values that can be sent to your SAP assessor along with the U value calculations we complete for you so the building fabric can be modelled at the earliest possible stage. This can then help to determine how your other potential measures such as MVHR, Solar PV, UFH and Air Source Heat Pumps will be incorporated.

This has certainly made the target fabric energy efficiency of the building a vital step in achieving SAP10 compliance.

Absolutely. The majority of our clients are looking to deliver thermally efficient, sustainable systems on time and on budget.

sip build uk self build homeWhen you combine the predictability of cost, program time and thermally efficiency of our systems we are ultimately part of the process in providing our clients with a streamlined route to compliance at the earliest possible stage which further reduces variables and risk whilst on site.

The ability to ensure that a building will achieve the required energy ratings whilst still in design stage allows for all additional measures such as MVHR, UFH and Solar PV to be factored into the design and engineering process of our SIPs system.

As building regulations become more onerous under Part L and SAP10 and the demand for responsibly sourced, sustainable systems increases our BBA approved SIP panels and Structural Timber Association Gold standard certification ensures we are perfectly placed to meet the demands of our growing client base.

SIPs are not limited to just new build houses; they can indeed be used for extensions. SIPs are a versatile building material known for their energy efficiency, strength, and quick installation time. Here are some points to consider when using SIPs for building extensions:

Self Build SIP projectCompatibility with Existing Structures: SIPs can be designed to integrate with existing buildings. However, it’s essential to ensure that the new extension is structurally compatible with the existing building. This may involve consulting with a structural engineer or an architect.  Through experience we have found that the better the existing building survey is the smoother the project runs. A precision-engineered building joining to an older traditionally built structure will have a few peculiarities!  To date we have yet to find an existing structure that we can’t join a new SIP structure too, however the devil is in the detail and the completion of a survey is a huge step in the right direction.

Energy Efficiency: One of the key advantages of SIPs is their high thermal efficiency, however, thought must be given to the original building.  Just because you end up with a shiny new high-performance part of the building, the huge benefits gained will dissipate very quickly if the existing building is not brought to a similar standard or the new extension cannot be compartmentalised internally to provide a new thermally efficient living area.

SIP panels also provide superb thermal efficiency while minimising the overall construction depth of wall build-ups – this can be a huge benefit to the homeowner that is looking to maximise the habitable space they can have with an extension.

internal view of SIP 172mm panels for both Walls and RoofSpeed of Construction: SIPs can significantly speed up the construction process because they come as pre-fabricated panels. This can be a big advantage if you want to minimize disruption during the extension process.  Achieving a weathertight structure quickly onsite allows for a reduction in site dust and disruption to the rest of the home.

Building Regulations and Planning Permission: Depending on your location, you’ll need to ensure that your extension with SIPs complies with local building regulations and planning permissions.

Cost Considerations: SIPs can be more expensive upfront compared to traditional building methods, however they can offer long-term savings through energy efficiency and reduced construction time. The cost savings due to improved speed on site may be less on smaller extensions than on larger self-build or residential projects so this must be a consideration.

Many SIP companies start with small extensions as they can offer more of a turnkey project approach which can be highly desirable for the homeowner.  Caution must be shown as smaller new businesses often require higher upfront payments which may put the homeowner at risk. This can often be coupled with the lack of required accreditations and certifications so due diligence should be completed. We recommend this with any size of SIP project!!

Due to years of experience, we understand that the need for an extension comes down to a small number of factors.

The need for space is a given but often moving to a larger home just isn’t financially viable.  Secondly you love your location and don’t want to move (but could afford to) and finally you buy a smaller house with the intention to add an extension to it.  The first instance which is generally budget-driven may not always be suitable for a SIP extension as a Timber Frame option would be beneficial from a budget point of view. Click here for Framebuild enquiry form /site

Where performance or speed of build is the driver SIP extensions can be very effective.  As a guide anything over 65/70m2 in size starts to become cost effective using SIPs – if the walls are SIPs and not all glazing!

In summary we have built many extensions over the last decade however we have also declined to price many as they are simply too small to benefit from the speed, thermal performance and precision that SIPs deliver.  If you are going out, up or both we can look at your proposed project and offer our opinion on the suitability of it and provide an estimate if it is suitable.

Remember Glass = Structure, Structure = Cost.

Plot selection is a critical part of any house building project. The characteristics of the plot significantly influence the design, construction and overall feasibility of the project. Here are some key points to consider:

  1. Size and Shape: The size and shape of plot determine the maximum footprint and layout of the building. It also influences factors such as setbacks, green space, and the potential for future expansions.
  2. Orientation: The orientation of the plot with respect to the sun and prevailing winds can impact on energy efficiency and comfort within the dwelling. Proper orientation allows for better utilisation of natural light and can contribute to passive heating and cooling strategies.
  3. Legal and Regulatory Constraints: Local zoning regulations, building regulations and other legal constraints may dictate what can and cannot be built on a particular plot. For example, building in a conservation area could be considerably more restrictive than an area designated for homes or even self build sites where unique designs are positively encouraged!
  4. Topography and Soil Conditions: The topography of the land and soil conditions affect the foundation design and construction methods. Steep slopes may require special considerations (Rock sockets, digging out of bedrock etc) and different soils may have varying bearing capacities. Conditions with lots of clay may need the foundations to be piled – has the budget included for this?
  5. Utilities and Infrastructure: Access to essential utilities such as water, electricity, and sewage systems is crucial. The availability and proximity of infrastructure can impact the overall cost and feasibility of the project. Please also factor in the frustration and cost when dealing with the utility providers!!!!
  6. Environmental Considerations: The plot’s surroundings and local ecosystem should be considered to minimize the environmental impact of the construction. We have seen a variety of wildlife impact the build process on site for example (but by no means the full list) has the site got bats, Great Crested Newts, Slow Worms or Badger sets?! All of these have stopped sites we have been involved with at some stage!
  7. Budget and Financial Considerations: The cost of the plot itself, as well as any necessary site preparation, should be factored into the overall budget of the project. Understanding the financial implications of the chosen plot is crucial for a successful project.

Once all the above is considered we then get to the heart of the matter!

You have found your plot, purchased it and appointed an architect – BUT will the site and access to it let you build the home you are dreaming of!!

Do not worry! We have built SIP superstructures in some of the most awkward and inhospitable of places. Our experienced operations team have helped build down alleyways, on top of hills, down tiny country tracks and on the top of existing buildings. Rear gardens, between two existing buildings and even party walls in London with single side access to name just a few! We have yet to find somewhere that we could not find a solution for (not that this is a challenge or gauntlet we are throwing down!)

 Best Private Housing Project of the Year