# NI Building Regulations, Technical Booklet F: Energy
Technical Booklet F is the energy efficiency bit, the one that decides how much insulation, how tight the building needs to be, and how efficient the kit has to run. It's NI's equivalent of England's Part L or Scotland's Section 6.
1. What Booklet F covers
- Limiting heat loss through walls, roofs, floors, windows and doors.
- Controlling air-leakage so you're not heating the street.
- Making sure systems are efficient · heating, hot water and fixed lighting.
- Using calculations (SAP / SBEM) to show the building hits overall energy and emissions targets.
This is where your insulation, U-values, air-test target and boiler/heat-pump spec all come from.
2. Targets and the "notional building"
Like the rest of the UK, NI's energy rules use a notional building · a model with set U-values, air-tightness and system efficiencies. Your design must perform as well as or better than this notional case.
The designer/SAP assessor will pick fabric specs, choose heating and hot water systems, set an air-tightness target, and add any renewables, until the calc says "this meets F."
Whatever they land on is what you're supposed to build.
3. Fabric, U-values and insulation
Booklet F gives back-stop U-values (worst-case limits) for external walls, roofs, ground floors, exposed floors, windows, doors and rooflights. The actual design may go better than those to hit the energy target.
On site:
- Don't thin down insulation because "it still looks decent" · match the type and thickness in the spec.
- Install insulation well · cut tight, no big gaps, no missing bits behind pipes or around joists.
- Make sure supplied windows and doors meet or beat the U-values on the design sheet, not just "looks similar."
Bad install can kill performance even if the drawings were good.
4. Air-tightness and ventilation
You'll nearly always have an air-test target baked into the design. The energy calcs assume a specific air-permeability value, plus either natural ventilation with fans or a mechanical system (MEV / MVHR).
On site:
- Treat the air-tightness line (linings, membranes, tapes) as a real thing · don't slash through it without sealing back up.
- Seal around windows, doors, service penetrations and junctions properly · not just foam and forget.
- Make sure everyone knows the target so they understand why you're so fussy about holes and gaps.
If you miss the air-test badly, you can fail F's performance target or have to spend time and money on remedial sealing and a retest.
5. Heating, hot water and lighting
Booklet F expects:
- Efficient heating · minimum efficiencies for boilers and low-carbon kit.
- Proper controls · time and temperature control, zoning where required.
- Hot water systems with insulated cylinders and pipes to limit losses.
- Reasonably efficient fixed lighting (in non-domestic and sometimes specified in residential).
On site:
- Don't swap a high-efficiency boiler or specified heat pump for a bargain-basement unit without checking what it does to compliance.
- Fit programmers, stats and TRVs as per spec · don't strip out controls because "the client will never use them."
- Insulate hot water cylinders and primary pipework as shown in the design, not just minimal lagging.
All of those details are plugged into the energy calcs that say "this passes F."
6. Thermal bridges and details
Junctions matter just as much as flat surfaces:
- Wall-to-floor, wall-to-roof, around openings, balcony supports, etc.
The designer may use default (worse) values or better values if they adopt detailed, low-bridge junction designs.
Your job:
- Follow any thermal bridge details · extra insulation wraps, thermal breaks, careful positioning of structure.
- Don't add big lumps of uninsulated structure not in the design.
- Keep continuity of insulation where the detail shows it · don't chop it for convenience.
7. How F fits into Building Control and sign-off
NI Building Control (district councils) will:
- Check the energy design (SAP/SBEM summary, specs) when they assess the plans.
- At the end, ask for: as-built SAP/SBEM, air-test results, evidence of insulation, systems and controls installed as specified.
If you've quietly downgraded insulation, windows, boilers, controls or PV: it may show up here.
8. How to stay out of trouble
At tender / pre-start
- Ask for the energy spec: U-values, air-tightness target, heating/renewables summary.
- Price what's actually in those documents, not just your usual "house build" spec.
During the build
- Police insulation quality like a hawk · bad install is the easiest way to blow performance.
- Treat membranes, tapes and seals as critical, not optional.
- Don't unilaterally change windows/doors, heating kit, or drop PV without a redesign and BC sign-off.
At the end
- Make sure the air-test is done and any holes are fixed before retest.
- Give the energy assessor correct "as-built" info so the final SAP/SBEM can be issued cleanly.
If you see Booklet F as a set of promises made in the energy design, your job is to build in a way that keeps those promises true: not nibble away at them for short-term savings.
What to do next
- Read: Working in Northern Ireland · building regulations overview
- Read: NI Building Regulations · Technical Booklet E: Fire safety
- Read: Scottish Building Standards · Section 6: Energy (for comparison)
- Read: Working in Wales · energy, Part L and Future Homes (for comparison)
Sources
- Building Regulations (Northern Ireland) Order 1979 · primary legislation.
- Technical Booklet F (NI) · Conservation of fuel and power.
- SAP / SBEM · energy calculation methodologies.
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