Material Change of Use (Conversions)

Material Change of Use is required under Building Regulations if you are proposing to carry out a barn conversion or forming flats/dwellings from an existing building.

Material Change of Use schemes need to comply with Approved Document L1B.

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Material Change of Use – Barn Conversions

Barn conversions come under the guidance Approved Document L1B and are not as difficult to achieve compliance as newly erected dwellings, however they do need to achieve compliance for U-values, heating systems and ratios of glazing (they should be designed on the same principle as domestic extensions).

The following U-values are as set out in Approved Document L1B :

Table I Standards for Controlled Fittings
Fitting	Standard
Window, Roof Window, or Rooflight	WER Band C or Better (see paragraph 4.22), or U-Value 1.6 W/m².K
Doors with >50% of Internal Face Glazed	U-Value = 1.8 W/m².K
Other Doors	U-Value = 1.8 W/m².K

Table II – Standards For New Thermal Elements (For New Build elements as part of the conversion schemes and extensions)
Elements¹	Standard (W/m² .K)
Wall	0.28²
Pitched Roof – Insulation At Ceiling Level	0.16
Pitched Roof – Insulation At Rafter Level	0.18
Flat Roof or Roof with Integral Insulation	0.18
Floors³	0.22⁴
Swimming Pool Basin	0.25
Notes: ‘Roof’ includes the roof parts of dormer windows, and ‘wall’ includes the wall parts (cheeks) of dormer windows. Area-weighted average values. A lesser provision may be appropriate where meeting such a standard would result in a reduction of more than 5% in the internal floor area of the room bounded by the wall. A lesser provision may be appropriate where meeting such a standard would create a significant problem in relation to adjoining floor levels. The U-Value of the floor of an extension can be calculated using the exposed perimeter and floor area of the whole enlarged dwelling.

Table III – Upgrading Retained Thermal Elements (Applicable to the existing thermal elements of the proposed scheme)
Element¹	(a) Threshold U-Value W/m 2.K	(b) Improved U-Value W/m 2.K
Wall – Cavity Insulation²	0.70	0.55
Wall- External or Internal Insulation³	0.70	0.30
Floor^{4 5}	0.70	0.25
Pitched Roof – Insulation at Ceiling Level	0.35	0.16
Pitched Roof – Insulation Between Rafters⁶	0.35	0.18
Flat Roof or Roof with Integral Insulation⁷	0.35	0.18
‘Roof’ includes the roof part of dormer windows and ‘wall’ includes the wall parts (cheeks) of dormer windows. This applies only in the case of a wall suitable for the installation of cavity insulation. Where this is not the case, it should be treated as ‘wall – external or internal insulation’. A lesser provision may be appropriate where meeting such a standard would result in a reduction of more than 5% in the internal floor area of the room bounded by the wall. The U-Value of the floor of an extension can be calculated using the exposed perimeter and floor area of the whole enlarged building. A lesser provision may be appropriate where meeting such a standard would create significant problems in relation to adjoining floor levels. A lesser provision may be appropriate where meeting such a standard would create limitations on head room. In such cases, the depth of insulation plus any required air gap should be at least to the depth of the rafters, and the thermal performance of the chosen insulant should be such as to achieve the best practicable U-Value. A lesser provision may be appropriate if there are particular problems associated with the load-bearing capacity of the frame of the upstand height.

Discreet changes were made in the October 2010 L1B document concerning Material Change of Use – conversion schemes should now have a glazing ratio of 25% to the proposed floor area. This can be problematic for conversion schemes which have existing openings in excess of this guidance, while reducing openings may affect [not effect] planning permission, ventilation requirements and means of escape.

From a thermal calculation point of view, if Building Control has asked for a justification of excess openings, then trade-off calculations need to be carried out. Trade-off calculations involve undertaking a primary set of calculations with the correct openings and correct U-values. This then gives a DER (Dwelling Emission Rate) to compare your proposed scheme against CO2 emissions. A secondary calculation is then carried out, based on the actual amount of openings and proposed U-values. As long as the proposed scheme is equal to or no worse then the notional calculation then this achieves Building Regulations [Regulations not Regulation] compliance.

In addition, when carrying out barn conversions it is fairly common for the client to incorporate an exposed external wall for feature purposes. This can be calculated and justified using the above guidance.

Heating systems play a large part in the DER calculation process. For example, the use of an air source heat pump will offset a lot more glazing/openings than a traditional oil boiler system. This is due to the fuel factor, given in SAP 2009 document ‘Standard Assessment Procedure’.

Formation of flats/dwellings under Material Change Of Use

If you are forming more, or fewer, dwellings from an existing building, irrespective of its previous use as domestic or non-domestic, this is also classed as Material Change of Use under Building Regulations. As shown above, U-values come under the guidance of Approved Document L1B. The U-values need to comply with the guidance unless their existing U-values are equal to or lower than the following:

Table I Standards for Controlled Fittings
Fitting	Standard
Window, Roof Window, or Roof light	WER Band C or Better (see paragraph 4.22), or U-Value 1.6 W/m².K
Doors with >50% of Internal Face Glazed	U-Value = 1.8 W/m².K
Other Doors	U-Value = 1.8 W/m².K

Table II – Standards For New Thermal Elements
Elements¹	Standard (W/m² .K)
Wall	0.28²
Pitched Roof – Insulation At Ceiling Level	0.16
Pitched Roof – Insulation At Rafter Level	0.18
Flat Roof or Roof with Integral Insulation	0.18
Floors³	0.22⁴
Swimming Pool Basin	0.25
Notes: ‘Roof’ includes the roof parts of dormer windows, and ‘wall’ includes the wall parts (cheeks) of dormer windows. Area-weighted average values. A lesser provision may be appropriate where meeting such a standard would result in a reduction of more than 5% in the internal floor area of the room bounded by the wall. A lesser provision may be appropriate where meeting such a standard would create a significant problem in relation to adjoining floor levels. The U-Value of the floor of an extension can be calculated using the exposed perimeter and floor area of the whole enlarged dwelling.

Table III – Upgrading Retained Thermal Elements
Element¹	(a) Threshold U-Value W/m 2.K	(b) Improved U-Value W/m 2.K
Wall – Cavity Insulation²	0.70	0.55
Wall- External or Internal Insulation³	0.70	0.30
Floor^{4 5}	0.70	0.25
Pitched Roof – Insulation at Ceiling Level	0.35	0.16
Pitched Roof – Insulation Between Rafters⁶	0.35	0.18
Flat Roof or Roof with Integral Insulation⁷	0.35	0.18
‘Roof’ includes the roof part of dormer windows and ‘wall’ includes the wall parts (cheeks) of dormer windows. This applies only in the case of a wall suitable for the installation of cavity insulation. Where this is not the case, it should be treated as ‘wall – external or internal insulation’. A lesser provision may be appropriate where meeting such a standard would result in a reduction of more than 5% in the internal floor area of the room bounded by the wall. The U-Value of the floor of an extension can be calculated using the exposed perimeter and floor area of the whole enlarged building. A lesser provision may be appropriate where meeting such a standard would create significant problems in relation to adjoining floor levels. A lesser provision may be appropriate where meeting such a standard would create limitations on head room. In such cases, the depth of insulation plus any required air gap should be at least to the depth of the rafters, and the thermal performance of the chosen insulant should be such as to achieve the best practicable U-Value. A lesser provision may be appropriate if there are particular problems associated with the load-bearing capacity of the frame of the upstand height.

Please contact us for advice or if you have any questions regarding conversions schemes or Material Change of Use.

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