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A basement-level space against a steel sheet-piled retaining wall in a UK construction, the zigzag steel profile lit by soft daylight from an opening above.

Application

Piling and below-ground walls: the profile followed, the cold and the damp kept on the other side.

Steel sheet piling, contiguous or secant piles, poured or precast concrete, blockwork and stone, all below ground and all cold and damp on their inner face. Closed-cell foam follows the profile no board can, and controls vapour as it insulates.

Start a project brief What it costs: the cost guide
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Is this your wall?

01The build-up

The pile stays. The layer follows it, flat-faced, from inside.

A sheet-piled wall is a deep corrugation running top to bottom, in contact with cold, wet ground on one side and a heated space on the other. No board fits it, and the ground never lets up. Switch the drawing between the bare pile and the sprayed pile.

Two states. Switch between them; the marks and the reading follow.

Swipe across to see the whole section.

BARE PILE · COLD GROUND, WET FACESection, schematic, not to scale. Three marks in each state; the cards beneath read them.

Cold steel · ground temperatureThe dew point · water formsAbove the dew point · dry

1The steel pile

Ground temperature, all year.

Steel in contact with the earth sits at ground temperature, well below the dew point of the air in a heated basement. Its inner face is the coldest surface in the building and the first to run wet.

2Ground, cold and wet

Constant pressure, constant moisture.

Below ground the moisture does not come and go with the weather. Groundwater and damp earth sit against the wall permanently, so vapour control is not optional. A board with open joints lets that vapour straight through.

3Water on the inner face

It runs down and pools at the slab.

Condensation on a pile runs to the floor and sits at the slab junction. The steel corrodes, the finishes fail and the space smells of damp.

The short version: below ground the problem is permanent and the substrate is a shape no board fits. A sprayed closed-cell layer follows the pile, closes the air gap and controls vapour in one material. The rest of this page is how it goes on properly.

02The order of work

Five steps, from inside the wall.

The work is done from the basement or excavation side, with the ground and any waterproofing untouched. Each step is checked before the next begins. HOLVEM has insulated piled and retaining walls for years; this is one of the applications a board cannot do.

  1. Substrate and waterproofing

    The pile or wall is inspected: profile, corrosion, running water, the state of the clutches or joints, and how the wall is drained or waterproofed. Foam is not a waterproofing system; where water is running in, that is dealt with first.

    HOLVEM checksFree-draining or waterproofed; no running water on the face.

  2. Preparation and protection

    Loose scale, corrosion product, soil and laitance come off the face. Drainage channels, sumps and service penetrations are protected. The slab is sheeted.

    HOLVEM checksClean, keyed face; drainage and services protected.

  3. Passes and depth

    Closed-cell foam is sprayed into the profile in passes, filling the pans first, then built out to a flat face at the specified depth. It bonds to steel, concrete, blockwork and stone alike. Closed-cell cures fast, so the wall is walked away from finished the same day.

    HOLVEM checksApplied thickness measured and recorded, panel by panel.

  4. Coating, where specified

    Where the foam stays exposed in an occupied basement and a reaction-to-fire classification is required, an intumescent coating is applied. Where a lining follows, the lining usually carries the requirement.

    HOLVEM checksCoverage logged where a coating is specified.

  5. Terminations

    The slab junction, the capping beam, service penetrations and any drainage detail are closed per project. The layer stops at a closed, coated edge and never covers a drainage path.

    HOLVEM checksEvery stop closed; every drain still open.

A close detail of bare steel sheet piling seen from the inside, the deep zigzag profile, rust bloom on the steel and a dark tide line of damp near the floor.
BeforeThe bare pile, from inside
The substrate as it is inspected: the depth of the profile, the state of the steel and the damp line that says where the water sits.

Every step is checked before the next. Thickness measured, coverage logged, compiled into a QA record at completion.

03Preparation

Before the first pass: what the wall has to be.

Below ground the substrate and the water decide everything. Three things HOLVEM establishes first.

Drained or waterproofed

Foam is not the waterproofing.

Running water, weeping clutches and a wet face are dealt with by the drainage or waterproofing design first. The layer goes on a wall that is managing its water, and never covers the path the water is meant to take.

Clean and keyed

Adhesion on steel, concrete or masonry.

Scale, corrosion product, soil and laitance come off. Closed-cell bonds to all of these substrates once they are clean; the bond is what makes the vapour control continuous.

Detailed

The slab, the capping beam and the services.

Where the layer stops and how it meets the floor, the beam above and every penetration is drawn per project before the work starts, and checked on the day.

Survey, or photographs?How HOLVEM works: we understand your project before we price it

04Thickness and objective

The depth is set by what the wall has to do.

Three objectives, three depths, each confirmed on your wall by the analysis. Below ground the vapour case usually sets the minimum. What it costs is on the cost guide, not here.

25 mmCondensation and vapour control

Keep the inside face dry.

Enough to put the face the air touches above the dew point and to give a continuous vapour control layer across the whole profile. The objective for plant rooms, stores and car parks below ground.

50 mmHeat retention

A basement that holds its heat.

Controls condensation and vapour and keeps warmth in an occupied lower floor.

75 mm and aboveA calculated U-value

A figure to meet, and to prove.

Set by the U-value the project has to reach, calculated for the wall as built against the ground. Specified per project and confirmed by the calculation.

A steel sheet-piled basement wall with a continuous cream closed-cell layer filling the profile and finished to a flat face, stopped cleanly at the floor slab, soft even light.
AfterThe layer, flat-faced over the pile
The finished face: the profile filled, a flat face at the specified depth, the stop at the slab closed.

Thickness and objectiveWhat it costs: the cost guide

05Where it suits

The buildings with walls below ground.

Piling and retaining walls sit under car parks, plant rooms, basements and infrastructure. Three building pages where this application is common.

Building

Car parks and undercrofts

Piled and retaining walls around basement car parks and the concrete soffits above them, insulated together.

Read the building page

Building

Data centres

Below-ground plant and technical spaces against piling where condensation and vapour control are non-negotiable.

Read the building page

Building

Offices and commercial

Basement floors under office buildings turned into usable, dry space against the retaining wall.

Read the building page

Every building type HOLVEM works on

06What HOLVEM checks

Three things checked before anyone talks about depth.

HOLVEM does not quote a depth from a photograph. The wall is understood first: how moisture moves through it, whether fire performance is required, and what U-value it must reach.

Condensation risk analysis

Will the inner face stay dry against the ground?

A condensation risk analysis to BS EN ISO 13788 for the wall as built, with ground conditions on one side and the internal conditions the space actually runs at on the other. Where the simple method is inconclusive, HOLVEM runs a dynamic simulation to BS EN 15026.

Fire

Is a reaction-to-fire classification required?

Where the foam remains exposed in an occupied space and a classification is required, the coated closed-cell system is specified, classified B-s2,d0 in the build-up tested. Where a lining follows, the lining usually carries it. Established before the depth.

U-value

What figure does the wall have to reach?

Calculated to BS EN ISO 6946 for this build-up against the ground, not read off the foam's own conductivity. The calculation is yours to keep.

Condensation risk analysisU-values and Approved Document LFire performance and coatings

07Straight answers

Ask us the hard ones.

The questions people with a piled or below-ground wall actually ask on the call, answered the way the specialist answers them.

Will spray foam waterproof my basement?
No, and nobody should tell you it will. Closed-cell foam controls vapour and stops condensation on the inner face; it is not a waterproofing or tanking system. Running water is dealt with by the drainage or waterproofing design first, and the layer never covers a drainage path.
Why not insulation boards?
A sheet pile is a deep profile with clutches, and a board cannot follow it. Whatever is left behind the board is an air gap against cold, wet steel, and that is where the condensation goes. Sprayed foam fills the profile and builds out to a flat face.
Does it stick to steel that has rusted?
Loose scale and corrosion product come off first; the foam then bonds to the sound steel beneath. The bond is checked as the work proceeds, because a continuous bond is what makes the vapour control continuous.
Can you work while the building is in use?
Usually. The work is from inside, panel by panel, with the area sheeted and protected. Where the space is a live car park or plant room it is sequenced around its use.
How do you prove it was done properly?
Applied thickness is measured and recorded, coverage is logged, and the evidence is compiled into a QA record handed over at completion.

The next step

Your wall.
Your brief.
A specialist.

If you already know the thickness or U-value you need, we price to it and confirm it is right; if not, we work it out with you. Tell us what the wall is, how it is drained and what the space will be used for. Photographs of the inner face are the most useful thing you can send.

Start a project brief Send photographs first

Or call . Enquiries received before 3pm on a working day are contacted the same day. After 3pm, the next working day. We understand your project before we price it.