L1 Elemental Method (ADL1 paragraphs 1.3–1.15)

“The Elemental Method can be used only when the heating system will be based on an efficient gas or oil boiler, on a heat pump, on community heating with CHP or on biogas or biomass fuel, but not for direct electric heating or other systems.” (ADL1, paragraph 1.2).

"When using the Elemental Method, the requirement will be met for new dwellings by selecting construction elements that provide the U-value thermal performances given in Table 1." (ADL1, paragraph 1.3).

The L1 Elemental Method lays down three requirements: a Heating Efficiency Requirement, a U-value (Table 1) Requirement and a Glazing and Door Area Requirement. The ‘additional requirements’ of L1 – ADL1 paragraphs 1.30-1.45, referred to in the Summary Guide as ‘Additional checks by builders’ – are, for convenience, also treated here under the heading of the Elemental Method.

“The Elemental Method can be used only when the heating system will be based on an efficient gas or oil boiler, on a heat pump, on community heating with CHP or on biogas or biomass fuel, but not for direct electric heating or other systems.” (ADL1, paragraph 1.2).

"Reasonable provision for boiler efficiency would be demonstrated by using a boiler with SEDBUK not less than the appropriate entry in Table 2." (ADL1, paragraph 1.7).

"For boilers for which SEDBUK is not available, the appropriate seasonal efficiency value from Table 4b of the SAP may be used instead." (ADL1, note to Table 2).

The heating system data used by the Part L1 analysis is all contained on the Heating System tab of the Part L Building & System Data. The fields labelled in black apply to the Elemental and Target U-value Methods. The following types of system are eligible for the Elemental Method:

·       Systems for which the box ‘Biomass or biogas fuel?’ is ticked.

·       Central heating systems with ‘Heating system type’ set to ‘Heat pumps’ (but not warm-air systems powered by heat-pumps).

·       Community heating schemes of all types. (The term CHP in ADL1 paragraph 1.2 – cited above – encompasses community heating schemes using waste heat from power stations; schemes using community boilers are deemed to be covered by the clause ‘based on an efficient gas or oil boiler’.)

·       Central heating systems using a gas or oil boiler with a suitable efficiency.

For central heating systems using a gas or oil boiler, the efficiency (normally a SEDBUK value) must be greater than the appropriate value from ADL1 Table 2 (78% for mains natural gas, 80% for LPG, 85% for oil (non-combi), 82% for oil (combi)).

If a SEDBUK value is not available (as indicated by the ‘SEDBUK’ check-box), an efficiency is taken from SAP Table 4b, using data entered in the ‘Boiler type’ boxes (‘Enter manufacturer’s efficiency?’ must be un-ticked). Note that in this context, the SAP Table 4b boiler efficiency is not modified by adjustments for control or distribution systems from SAP Table 4c.

"When using the Elemental Method, the requirement will be met for new dwellings by selecting construction elements that provide the U-value thermal performances given in Table 1." (ADL1, paragraph 1.3).

For each heated room, all heat-loss elements are subjected to the U-value checks set out in paragraph 1.3 and Table 1.

The Table 1 category ‘Pitched roof with insulation between rafters’ is applied to ceiling elements linking to rooms of type ‘Unheated space with pitched roof and insulation between rafters’.

The Table 1 category ‘Pitched roof with insulation between joists is applied to ceiling elements linking to rooms of type ‘Unheated space with pitched roof and insulation between joists.

Ceilings linking to other types of unheated space, and roof elements, are treated as belonging to the category ‘Flat roof or roof with integral insulation’. This is a combination of the Table 1 categories ‘Flat roof’ ‘and ‘Pitched roof with integral insulation’, which have the same U-value requirement.

In the case of windows, roof windows and doors the check is applied to an area-weighted average U-value for the whole building. The U-value requirement in Table 1 depends on the type of frame (metal or wood/PVC). In cases where there is a mixture of frame types the required U-value is set to the value appropriate to the type of frame accounting for the greater overall area, as stipulated in a reply posted on the BRE FAQ website^[10].

Elements defined as walls in ModelIT are treated as roofs if they have a slope less than 70 degrees, and elements defined as roofs in ModelIT are treated as walls if they have a slope greater than or equal to 70 degrees. The same principle applies to windows and rooflights.

Table 1 note 2 is applied to elements with a slope of between 10 and 70 degrees in rooms of type ‘Room-in-the-roof as material alteration’.

For link-exposed elements BS EN ISO 13789^[7] is applied in all cases. See ADL1 paragraph 0.8 and SAP 2001^[8]  paragraph 3.3.

"The requirement would be met if ... the area of the windows, doors and rooflights together does not exceed 25% of the total floor area." (ADL1, paragraph 1.8).

Areas of windows, doors and rooflights include frames. Total floor area is gross internal area, in accordance with ADL1 paragraph 0.15.

L1 stipulates additional requirements relating to:

Limiting thermal bridging at junctions and around openings (ADL1, paragraph 1.30-1.32)

Limiting air leakage (ADL1, paragraph 1.33-1.35)

Space heating system, zone, timing and boiler controls (ADL1, paragraph 1.36-1.41)

Hot water systems (ADL1, paragraph 1.42-1.46)

Commissioning of heating and HWS systems (ADL1, paragraph 1.47-1.50)

Operating and maintenance instructions for heating and hot water systems (ADL1, paragraph 1.51)

These requirements cannot be analysed in software but are included for completeness.