What are your self-buid superstructure methods?
The word “superstructure” simply means everything built above ground level: the walls, frames, floors, and roof that form the skeleton of your house. When you choose a construction method, you’re choosing your superstructure. It’s one of the most important decisions in your project because it dictates not only how your home is built but also how it will perform, how long it will take, how much it will cost, and how lenders will view it.
Think of the superstructure as the backbone of your build. It holds everything else up: insulation, plaster, finishes, electrics, plumbing, windows, and doors. The system you select influences what your house will feel like to live in. A masonry house feels solid and heavy; a timber frame house feels warm and fast to build; a SIPs house feels ultra-tight and efficient. None is inherently better; each has strengths and weaknesses. The right choice depends on your budget, your site, and your priorities. But what are your choices?
Masonry Superstructure
Masonry remains the UK’s default choice. Over 70% of homes are still built this way, using a combination of blockwork, brick, mortar, and insulation. It’s a system most planners understand, most builders are trained in, and most lenders feel comfortable with.
How it works
Most modern masonry construction is built as a cavity wall consisting of an outer facing or cladding leaf. This cavity usually contains some form of insulation and an inner leaf of blockwork. The outer leaf can be made of brick, stone, or blockwork. If it is blockwork, then it is usual for this to be harled or rendered, but it may sometimes be clad with either timber or uPVC. This outer leaf is not load-bearing, although it provides much of the wall's stability, as it is tied to the inner leaf with stainless-steel wall ties that extend through the wall into the building's interior.
Nowadays, it is used to provide much of the insulation for walling. Full-fill cavity insulation uses mineral or glass-fibre wool batts that are installed into the cavity as work progresses. The wider the cavity, the more insulation it contains, and the higher its thermal efficiency. Partial-fill insulation is used in high-exposure situations, where it is advisable or necessary to keep a clear cavity to allow water to drain away if the facing bricks become saturated. This type of insulation utilises dense and rigid foam boards that are secured against the inner leaf of the wall using special clips on the wall ties. The inner leaf of the wall is constructed from blocks, which may be either dense aggregate blocks with high load-bearing capability but low thermal efficiency, or lightweight aggregate blocks with much higher thermal efficiency but lower strength. The inner leaf supports the primary loadings and bears the weight of the roof. Openings within the walls must have lintels above them to support the upper brick and blockwork. These lintels are typically made of steel and either contain insulation or allow the standard cavity-wall insulation to be maintained over the gap, thus avoiding cold spots or 'cold bridging'. The bridge in the cavity, down each side of the reveal, is insulated using a cavity closer that also prevents damp from crossing the cavity. Masonry walls are robust enough to support beam-and-block or concrete suspended floors initially, as well as other floor levels. Most builders and subcontractors understand the concept of traditional masonry construction, giving the self-builder a fairly broad choice. It is a highly divisible sequence, with many trades needing to coordinate within the day, sometimes within the hour, making it quite management-intensive.
Strengths
Proven track record: centuries of use in the UK.
Durability: long-lasting and low maintenance.
Wide skills base: most trades know how to build in masonry.
Design flexibility: easy to adapt on site.
Planning acceptance: fits most local vernaculars.
Weaknesses
Slower and more weather-dependent than off-site systems.
Harder to achieve airtightness without meticulous detailing.
Heavier, requiring more robust foundations.
Modern upgrades: Today’s masonry walls include more insulation than in the past, and thermal bridging (heat lost through structural elements) must be carefully managed. Thin-joint blockwork and air-crete blocks can improve performance.
In practice: A couple in Cheshire wanted a traditional brick home. Masonry allowed them to match local red brick, making planning approval smoother. The build took 18 months, longer than timber frame alternatives, but the result blended seamlessly with neighbouring homes and felt substantial and timeless.
Insulated Concrete Formwork (ICF)
ICF is an increasingly popular choice for self-builders, especially on complex sites. It involves stacking hollow polystyrene blocks, a bit like Lego, and then pouring concrete into the void. The polystyrene remains in place, acting as insulation, while the concrete provides structure.
How it works:
This method of building utilises hollow polystyrene blocks that fit together, much like a giant Lego set, and are assembled on-site. The blocks are then filled with concrete, often with reinforcement bars running through the structure. In some ways, it is similar to the concrete formwork used to construct motorway bridges, except that here the formwork is left as the insulation for the wall. Most ICF companies run training days, enabling self-builders to construct their own super. The filled blocks can be rendered on the outside and plastered on the inside, thus creating a ready, insulated, and very airtight structure. Care must be taken when pouring the concrete to prevent hydraulic pressures from bursting the joints or creating voids. Because the concrete is insulated throughout the curing process, it can be poured in colder conditions than would typically be acceptable. The combination of lightweight, easy-to-handle blocks and poured concrete makes this a quick, all-weather construction system. On a straightforward project, the formwork and pour for a single storey can be completed in as little as two or three days; much faster than traditional masonry, Plus, the insulating blocks help to retain heat when the concrete is pumped in - so the cure can still take place even in very wet or frosty conditions that might put the clappers on a brick-and-block build.
With ICF, the polystyrene formwork used to contain the concrete pour remains in place permanently - providing an instant double thickness of insulation. When specified to the proper depth, this built-in thermal protection can easily achieve U-values as low as 0.11 W/m²K (compared to the Building Regulations' upper limit of 0.30 W/m²K). That means good heat retention and minimal energy bills. And it can also be used for basements.
Strengths
Strength: suitable for basements, retaining walls, and sloping sites.
Thermal mass: concrete stabilises internal temperatures.
Energy efficiency: thick insulation built in.
Speed: blocks are lightweight and easy to stack before the pour.
Weaknesses
Concrete has a high carbon footprint.
Requires skilled contractors to ensure pours are consistent.
Wall thickness can reduce internal floor area.
Fewer UK builders have ICF experience compared to masonry.
Costs: Comparable to timber frame, sometimes higher than masonry. Gains often come in speed and performance rather than headline price.
Concrete Systems
Beyond ICF, other concrete systems exist. These are less common in self-build but worth understanding.
Cast-in-situ involves shuttering (temporary moulds) erected on site, into which concrete is poured. It delivers incredible strength and can form unusual shapes but requires significant formwork and skilled teams.
Pre-cast concrete panels are manufactured in factories and craned into place. This system is fast and precise but more common in commercial projects than one-off homes.
Strengths
Unrivalled durability.
Fire resistance.
Acoustic performance.
Weaknesses
Heavy, requiring cranes and specialist skills.
High embodied carbon.
Less flexible for one-off, small projects.
Concrete systems shine in specific contexts: basements, retaining walls, and ultra-modern designs with exposed concrete finishes.
Timber Frame
Timber frame is the leading alternative to masonry in the UK and dominates in Scotland. Panels are prefabricated in factories, then delivered and erected on site.
How it works:
It is the inner skin of a cavity wall that supports the roof and gives the building its structural strength. In a timber-framed house, this is formed by panels that are usually prefabricated and then raised up into position and fixed together to form a rigid structure. The panels are manoeuvred from softwood timber framing over which a structural sheet material, such as plywood or oriented strand board (OSB, is fixed.
The insulation which fills the space between the studs is normally put in on site once the house is watertight. External windows and doors are typically fixed after the frame has been erected, but if they are included in the package deal, they would normally be fitted during the erection process.
Types
Open panel: basic frame with sheathing. Insulation and services fitted on site.
Closed panel: pre-insulated and sometimes pre-fitted with windows, speeding construction further.
Strengths
Rapid build ; a watertight shell can be achieved in weeks.
Precision from factory conditions.
Excellent airtightness potential.
Renewable material with lower embodied carbon than concrete.
Weaknesses
Requires early design freeze: openings and layouts must be decided before panels are made.
Susceptible to delays if factory slots are missed.
Perception (though outdated) that timber is less durable.
Green Oak Frame
Green oak frame construction harks back to medieval traditions but remains popular for self-builders wanting character and craft. It uses large oak beams, often exposed internally, joined with traditional joints.
How it works:
This is a 15th century building technique brought into the modern age with a massive skeleton of heavy Oak Timbers forming the frame. The important difference is that this frame is visible internally and externally and that the building is of a single skin construction. The spaces between the Oak Timbers on the external walls are filled in with urethane panels with galvanised perimeter trims and mesh reinforcement.
The sophisticated system of trims, waterbars, weather seals and drainage channels ensure the building meets proper standards and can deal with the British climate. Hybrid forms, which use the Oak frame as an internal leaf and then clad it with timber, brick, or even SIPs panels, are also popular.
Strengths
Stunning aesthetics: visible beams create a warmth and heritage feel.
Durability: Oak hardens over time.
Sustainability: Oak is renewable when sourced responsibly.
Weaknesses
Cost: labour-intensive and specialised.
Movement: green oak shrinks and cracks as it dries. This is normal, but design must allow for it.
Speed: slower than panelised systems.
Modern approach: Oak frames are often combined with infill panels (SIPs or timber frame) to meet energy standards. This hybrid gives the look of traditional craftsmanship with the performance of modern systems.
Structural Insulated Panels (SIPs)
SIPs are panels of rigid insulation sandwiched between structural boards, usually OSB. They combine structure and insulation in one product.
How it works:
These comprise two outer skins of oriented strand or MDF board sandwiching a polystyrene or polyurethane centre. They can be used in structural situations for both walling and roofing where they replace traditional stud panels and trusses.
They can either be delivered whole to site and have openings cut later, or manufactured off site to exact requirements. Only labour with specific knowledge should be used; best to rely on the manufacturer’s recommended installers.
Strengths
Ultra-high insulation values.
Exceptional airtightness.
Fast construction as panels slot together quickly.
Slim walls allow more internal space.
Weaknesses
Higher cost upfront.
Requires skilled installers.
Less flexibility once panels are manufactured.
Performance: SIPs can achieve Passivhaus-level standards more easily than many other building systems, making them an attractive option for low-energy builds.
Finance note: Some lenders are cautious with SIPs, but with the right warranty and evidence of quality, most accept them. Mayflower helps match SIPs projects to the right lenders.
Alternative Systems
While less common, several alternative systems are gaining attention.
Cob: A mixture of clay subsoil, aggregate or sand, fibre (usually straw) and water. Built up in layers until the desired wall height is achieved.
Rammed Earth: Layers of earth compacted in lifts, around 150mm at a time. Over-compaction can lead to cracking.
Straw Bale: Cost-effective, with thick walls that provide two to three times better insulation than conventional walls, but they are moisture-sensitive. Must be kept dry with overhangs and breathable renders.
Hempcrete & Lime: Mixes of hemp shiv and lime binders, or limecrete, also noted for ecological benefits.
For most self-builders, these systems remain more inspirational than practical. That said, sustainable innovation is pushing boundaries, and some alternative methods may enter the mainstream in coming years.
Cob
This is the mixture of clay subsoil, aggregate or sand, fibre (usually straw) and water. The mixture is compressed onto a low rock wall or plinth, and then trimmed on the side to create the profile line. COB is built up in layers until the desired wall height is achieved.
Rammed Earth
This method of construction involves compressing earth in layers, known as lifts. Each lift is approximately 150mm and is stamped from the top. Naturally the lifts are more compacted at the top, apart from the very upper crust that may be slightly loose due to the impact of the ramming head. Generally, the more compacted it is, the stronger it becomes, but excessive compaction can lead to cracking and weakening.
Straw Bale
Ever since straw baling machines emerged over a hundred years ago, people have been building with straw bales. The impact of this system on the environment is less and if rendered in clay or lime, the walls become a very healthy option. It is also very cost effective as the bales are relatively cheap and quick to assemble. The walls tend to be thicker than those of conventional building methods, but the insulation values are approximately two to three times better. Straw bale houses can be built to resemble traditional buildings. Still, one of the advantages of this construction method is that it can be sculpted to incorporate curves and other interesting shapes. Straw bale buildings are usually built on a plinth of some sort, either rock, brick, timber posts, concrete blocks, rammed earth or tyres. This plinth needs to be well insulated so that the benefits of the straw bales' natural insulation are not lost.
The walls are constructed in two main methods: load-bearing or infill frames. Load-bearing is the most cost-effective of the two systems in both time and expenditure, and is the most versatile in terms of creative designs, as it can incorporate more curves and does not require complex woodworking skills for frame construction. As straw bales are very sensitive to moisture, it is imperative to keep them dry at all times during and after construction. A good overhang on the finished roof of at least 500mm is necessary. During construction, you may want to cover all the walls with a tarpaulin or possibly even encapsulate the building temporarily until it is watertight. Services are installed in a very similar manner to conventional construction, but they will require an additional conduit sleeve to accommodate added heat or moisture.
All in all, this is a highly sustainable construction method, and when implemented correctly, it has a significantly low carbon footprint and delivers a healthy, efficient living space.
Lime
Lime has been used in building for thousands of years, especially in areas where limestone is available, but it lost its popularity when cement was invented. Cement is also made from limestone, but it is fired differently. When mixed with sand and stone, concrete is formed. Cement was cheaper and easier to use as it cured (set) quicker, and it has now all but dominated the market. The use of lime in construction has increased since it was recognised as a necessary product for the restoration of old buildings. The more it was used, the more apparent it became that it had many advantages over cement. Lime is soft, permeable and flexible. It has also proven to be more sustainable, as it has less embodied energy in its manufacture than cement and allows for some natural breathing. It also adds a sustainable element to brickwork and masonry by enabling their reuse. In contrast, cement-based products adhere to the bricks, making them almost unusable, or at the very least, they can only be broken up and used as fill.
Timber will last longer when used in conjunction with lime as it allows it to breathe and tends to draw water away from the wood and allow it to evaporate. Lime is a natural biocide that helps preserve timber and enables its use alongside other sustainable materials, such as straw, reeds, hemp, and clay. Burnt lime that has been heated until waterless is known as quicklime, calcium hydroxide (Ca(OH)2) or slaked lime. It reacts strongly with water to form hydrated lime and is typically sold as a dry hydrate. Hydraulic lime is lime that has been burnt with up to 22% clay and has been available in its natural form since the late 18th century. Artificial hydraulic lime is made with clinker or limestone fillers (which, strictly speaking, makes it a cement). It sets in wet conditions and is usually used as a plaster. Considerable damage has been caused to the restoration of old buildings that incorporated stonework with lime mortar by the use of cement-based products. The properties of lime and cement are different and this needs to be carefully considered before attempting any combined use.
Hemp
Many construction materials are made from hemp, with examples dating back to Roman times. The combination of a hemp and lime mix has been used as a replacement for wattle and daub in historic timber. It is likely to become far more prevalent in the United Kingdom due to its eco credentials and versatility. The growing of hemp has, for quite a while, been illegal due to its similarities with the drug cannabis. Industrial hemp, which is grown from seeds that are low in THC (Tetrahydrocannabinol), the psychotropic element, can look similar to the drug when in the field, but for anyone with ulterior motives, it would take a joint the size of a lamp post to get you high.
Today it is possible to grow hemp legally, and licenses are relatively easy to acquire, though the agricultural subsidies are very limited. In the past, hemp was required for rope and sail manufacture, and the original Levi’s jeans were made of hemp, but with the increase in nylon and other synthetic fibres, coupled with the legislative complications, the industry had all but faded. Recently though, there has been a revival as legislation has been eased, and it is now used for clothing, oils for cosmetics and foodstuffs, hemp resin composites (many prestige German cars have hemp door panels). In construction, it is usually mixed with lime or earth, known as hempcrete. It can be a solid wall, combined with timber frame, used as an infill in post and beam construction, cast as bricks or blocks, or used as an insulating plaster. The usual method is to cast the hempcrete into conventional timber frames. The hempcrete merely acts as a solid wall insulation and the frame still forms the structural integrity of the building.
In short, you have lots of options! For a specialist build, it’s always best to speak to an expert, like us at Mayflower Mortgage. Book in for a FREE, no obligation call today, and we will be happy to chat through your plans and get you on the right path.