ICF Help & Advice

Our insulated concrete formwork help & advice centre has been created as a reference and information hub for designing and building ICF structures in general, and Polarwall in particular.

ICF Basements
Basement when your budget is tight

When your budget is tight, building into the ground, with its cost uncertainty might mean that the prudential builder should forego the benefits a basement normally bestows.  Even a full geological site survey with several test holes can only ever paint a partial picture of what you may discover when you start digging.  We have seen unknown underground streams,  undocumented service pipes, archaeological items. the presence of which are felt extra keenly when you budget is tight.   

If you have close neighbours then there is a risk to the neighbouring structure from your hole in the ground.  To stop this then a piling solution may be required to hold back your neighbours home from falling into your hole.  The general rule is that the load from a structure spreads out at 45 degrees from the bottom corners of the foundation and you must not cut through this imaginary line.  See the drawing at the side for a sketch showing this load line.+ 

If you have a high water table on your site then a basement is not impossible but it can add to the cost. This increase in cost is not only for extra costs in waterproofing so much as the possible need to have to “de-water” the site during the construction. Such de-watering adds both time and cost to the build budget. AlsoIf you have poor access then extra costs might be incurred through movement of materials and also for removal of spoil from the dig-out.   

Basements as extensions.

If you are building an extension to an existing property, then a basement may seem like a good idea.  It rarely is as this will need underpinning under the existing house and underpinning can be very expensive.  You will need to underpin the existing structure to the length of the extension plus at least an extra metre to either side. For underpinning costs allow £1500 to £2000 per linear metre of underpinning. 

Sandy soils may look ideal for basements as these are usually well drained. However, when the sand has little cohesion and is described as “running sand” then the dig can take three times longer than a stiff clay soil and may require “battering back” to stop spillage. 

In essence, building a basement on a limited budget requires hard practical choices. However, if the above does not deter you then go for it. 


The various sections above cover the main topics for ICF construction both above and below ground. 

Do not use this as an alternative to what your chosen manufacturer recommends.  We can do things with Polarwall that ICF blocks can’t do and there may some things that you do with other ICFs that Polarwall can’t do. For example our instructions on vibrating the concrete may not be wise on some EPS block systems. 

We want to add to and develop this section, so we welcome all your questions, suggestions for topics and feedback.  If you want to go deeper into a topic please let us know.  This advice hub does not replace our training (or any other companies training) and you still need to avail yourself of our FREE training course.