Do modular homes have to meet Building Regulations?
Yes. The Building Regulations apply to the building, wherever its parts were made. A new dwelling needs either a full plans application or a building notice to the local authority or an approved inspector, inspections during the work, and a completion certificate at the end. That certificate is what a solicitor and a lender will ask for.
The difference with a factory-built house is evidence. The wall, roof and floor build-ups are fixed designs with published layers, so their performance is calculated once and documented, rather than depending on what was done on a wet site. Trident supplies those schedules and the material specifications; the site-specific parts, foundations, drainage and the energy calculation for your plot, are done by your designer or ours.
BOPAS: Accredited system, continuously evaluated · 60 years: Durability assessment · ISO 9001:2015: Quality managed factory · Class A1: Non-combustible insulation. See BOPAS and certificates.
Which garden rooms are exempt?
A detached building with no sleeping accommodation is exempt from the Building Regulations when its floor area is under 15 m². Between 15 m² and 30 m² it stays exempt if it is at least 1 m from every boundary, or is built substantially of non-combustible materials. Larger buildings, and anything used for sleeping, need an application.
Electrical work in an exempt building still has to comply with Part P. Whether the building also needs planning permission is a separate question, answered on the planning permission guide.
Guide last reviewed: . Summarised for England.
What does Part L require of a new home?
Part L sets a carbon and energy target for the whole dwelling, calculated with the government's SAP method, plus limiting fabric values that no element may be worse than. The limits below are from Approved Document L, Volume 1, 2021 edition, Table 4.1, in force for new dwellings in England since June 2022.
| Element | Limiting U-value (W/m²K) |
|---|---|
| External walls | 0.26 |
| Floors | 0.18 |
| Roofs | 0.16 |
| Windows, roof windows and doors | 1.6 |
Source: Approved Document L, Volume 1: Dwellings, 2021 edition, Table 4.1. Limiting values are a floor, not the target: the notional dwelling the target is based on performs better.
How a Trident envelope meets it
Non-combustible to Class A1, from 100 mm up to 200 mm within the frame plus a 50 mm counter-insulated layer that breaks the thermal bridge through the studs. The thickness is chosen for the building and its use, and the external wall insulation at each published build-up is:
- 100 mm build-up: 100 mm basalt wool
- 150 mm build-up: 150 mm basalt wool
- 200 mm build-up: 200 mm basalt wool
- 250 mm build-up: 50 mm + 200 mm basalt wool
The U-value of each element is calculated for the build-up agreed at quotation and submitted with the Part L calculation for your house. Garden buildings and the A-Frame publish theirs on the model page. Turnkey base includes the air-source heat pump; underfloor heating, mvhr ventilation, solar pv + battery are priced upgrades.
Every layer of every build-up is on the technology page; the energy options are on eco modular homes.
Which other parts matter for a timber-frame modular house?
The Approved Documents are lettered A to S. These are the ones a factory-built timber-frame home is most often asked about, and how the Trident system answers each.
Part A
Structure
The frame carries the loads. Calibrated, planed and kiln-dried softwood at 12–15% moisture content, so the frame behaves predictably under load and does not move after assembly.
Part B
Fire safety
Non-combustible to Class A1, from 100 mm up to 200 mm within the frame plus a 50 mm counter-insulated layer that breaks the thermal bridge through the studs. Separation distances to boundaries and the cladding specified for the site are checked at design stage.
Part C
Moisture
A breather membrane outside the insulation and a vapour control membrane inside it, so the build-up manages moisture in both directions across the life of the building.
Part F
Ventilation
Background and extract ventilation to the current requirement; mechanical ventilation with heat recovery (MVHR) is available as a priced upgrade.
Part L
Conservation of fuel and power
Fabric U-values, airtightness and the heating system together must meet the target for the dwelling. The air-source heat pump is inside the Turnkey base scope.
Part P
Electrical safety
Basic electrics under Turnkey base are installed, tested and certified by a registered electrician.
What does Trident provide for the application?
- Build-up schedules for external walls, roof and floor at the agreed insulation thickness
- Material specifications: C24 timber, basalt wool, OSB-3, Juta membranes
- Floor plans and elevations of the model, adapted where the design changes
- BOPAS and ISO 9001:2015 certificates for the lender and the warranty provider
- Under Turnkey base: installation, testing and handover of the services, with the certificates
What stays with you or your designer
The Building Regulations application itself, the SAP calculation for your plot, foundation design where you are not taking the Turnkey base foundation, drainage, and the inspector's fees. These sit outside every purchase option, alongside planning and surveys; the full list is on the price guide.
If you are building the shell yourself, the self-build page sets out the split in detail.
Regulations and performance: common questions
Is a garden room under 15 m² exempt from Building Regulations?
Yes, if nobody sleeps in it. From 15 m² to 30 m² it stays exempt when it has no sleeping accommodation and is either at least 1 m from every boundary or built substantially of non-combustible materials. Electrical work must still meet Part P.
What are the Part L limiting U-values for a new house?
External walls 0.26, floors 0.18, roofs 0.16 and windows or doors 1.6 W/m²K, from Approved Document L, Volume 1, 2021 edition, Table 4.1. These are limits an element may not exceed; the dwelling as a whole must also meet its energy target.
Who submits the Building Regulations application?
You or your designer, to the local authority or an approved inspector. Trident supplies the build-up schedules, material specifications and drawings the application needs; the SAP calculation and foundation design for your plot are done by your designer or ours.
Does the electrical work come with a certificate?
Yes. Under Turnkey base the basic electrics are installed, tested and certified by a registered electrician, which satisfies Part P and is what building control asks to see.
More answers on the full FAQ page.
Need the technical pack for an application?
Tell us the model and the plot. We will send the build-up schedules and certificates your designer or building control inspector will ask for.