SCOTTISH EXECUTIVE

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Building Regulations: Technical Standards

Example 1 - Pitched roof with insulation between ceiling joists or between rafters

Determine the thickness of the insulation layer required to achieve a U-value of:

0.25 W/m²K if insulation is between the joists, and
0.35 W/m²K if insulation is between the rafters.

diagram

For insulation placed between ceiling joists (U-value 0.25 W/m²K)

Using Table E1, from column D, row 2 of the table, the base thickness of insulation required is 170 mm.

The base thickness may be reduced by taking account of the other materials as follows from Table E4:

19 mm roof tiles	column D, row 13	= 1 mm
Roof space	column D, row 11	= 5 mm
10 mm plasterboard	column D, row 7	= 2 mm
Total reduction		= 8 mm

The minimum thickness of the insulation layer between the ceiling joists required to achieve a U-value of
0.25 W/m²K is therefore:

Base thickness less total reduction ie 170 _ 8 = 162 mm.

For insulation placed between rafters (U-value 0.35 W/m²K)

Using Table E1, from column D, row 4 in the table, the base thickness of insulation required is 103 mm.

The reductions in the base thickness are obtained as follows from Table E4:

19 mm roof tiles	column D, row 13	= 1 mm
10 mm plasterboard	column D, row 7	= 2 mm
Total reduction		= 3 mm

The minimum thickness of the insulation layer between the rafters required to achieve a U-value of 0.35 W/m²K is therefore:

Base thickness less total reduction ie 103 — 3 = 100 mm.

Example 2 - Pitched roof with insulation between and over ceiling joists

Determine the thickness of the insulation layer above the joists required to achieve a U-value of 0.25 W/m²K for the roof construction shown below:

diagram

It is proposed to use mineral fibre insulation between and over the joists with a thermal conductivity of 0.035 W/mK.

Using Table E2, from column E, row 2 of the table, the base thickness of insulation layer = 152mm.

The base thickness may be reduced by taking account of the other materials as follows from Table E4:

19 mm roof tiles	column E, row 13	= 1 mm
Roof space	column E, row 11	= 6 mm
10 mm plasterboard	column E, row 7	= 2 mm
Total reduction		= 9 mm

The minimum thickness of the insulation layer over the joists required in addition to the 100 mm insulation between the joists to achieve a U-value of 0.25 W/m²K is therefore:

Base thickness less total reduction ie 152 — 100 — 9 = 43 mm.

Example 3 - Industrial roof with outer sheeting

Determine the thickness of the insulation layer required to achieve a U-value of 0.45 W/m²K for the roof construction shown below.

diagram

Using Table E3, from column E, row 6 of the table, the base thickness of the insulation layer is 73 mm.

The base thickness may be reduced by taking account of the other materials as follows from Table E4:

Outer sheeting (negligible) 12 mm Calcium Silicate liner board	column E, row 10	= 2 mm
Total reduction from base level thickness		=2 mm

The minimum thickness of the insulation layer required to achieve a U-value of 0.45 W/m²K is therefore:

Base thickness less total reduction ie 73 — 2 = 71 mm.

Example 4 - Concrete deck roof

Determine the thickness of the insulation layer required to achieve a U-value of 0.45 W/ m²K for the roof construction shown below.

diagram

Using Table E3, from column D, row 6 of the table, the base thickness of the insulation layer is 62 mm.

The base thickness may be reduced by taking account of the other materials as follows from Table E4:

3 layers of felt	column D, row 14	= 1 mm
150mm concrete deck column D, row 3 adjusted for 150 mm thickness (1.5 x 9)		= 14 mm
Total reduction from base level thickness		= 15 mm

The minimum thickness of the insulation layer required to achieve a U-value of 0.45 W/m²K is therefore:

Base thickness less total reduction ie 62 - 15 = 47 mm.

WALLS

Table E5 to Part J Appendix E: Base thickness of insulation layer

		Thermal conductivity of insulant (W/mK)
		0.02	0.025	0.03	0.035	0.04	0.045	0.05
Design U-value (W/m²K)		Base thickness of insulating material (mm)
	A	B	C	D	E	F	G	H
1	0.30	63	79	95	110	126	142	158
2	0.35	54	67	80	94	107	120	134
3	0.40	46	58	70	81	93	104	116
4	0.45	41	51	61	71	82	92	102
5	0.60	30	37	45	52	59	67	74

Table E6 to Part J Appendix E: Allowable reduction in base thickness for common components

		Thermal conductivity of insulant (W/mK)
		0.02	0.025	0.03	0.035	0.04	0.045	0.05
Design Component		Reduction in base thickness of insulating material (mm)
	A	B	C	D	E	F	G	H
1	Cavity (25 mm min.)	4	5	5	6	7	8	9
2	Outer leaf brick	2	3	4	4	5	6	6
3	13 mm plaster	1	1	1	1	1	1	1
4	13 mm lightweight plaster	2	2	2	3	3	4	4
5	10 mm plasterboard	1	2	2	2	3	3	3
6	13 mm plasterboard	2	2	2	3	3	4	4
7	Airspace behind
	plasterboard dry-lining	2	3	3	4	4	5	6
8	9 mm sheathing ply	1	2	2	2	3	3	3
9	20 mm cement render	1	1	1	1	2	2	2
10	13 mm tile hanging	0	0	0	1	1	1	1

Table E7 to Part J Appendix E: Allowable reduction in base thickness for concrete components

		Thermal conductivity of insulant (W/mK)
		0.02	0.025	0.03	0.035	0.04	0.045	0.05
	Density (kg/m³)	Reduction in base thickness of insulation (mm) for each 100 mm of concrete
	A	B	C	D	E	F	G	H
Concrete inner leaf
1	600	9	11	13	15	17	20	22
2	800	7	9	11	13	15	17	19
3	1000	6	8	9	11	12	14	15
4	1200	5	6	7	9	10	11	12
5	1400	4	5	6	7	8	9	9
6	1600	3	4	4	5	6	7	7
Concrete outer leaf or single leaf wall
7	600	8	10	13	15	17	19	21
8	800	7	8	10	12	14	15	17
9	1000	6	7	8	10	11	12	14
10	1200	4	6	7	8	9	10	11
11	1400	3	4	5	6	7	8	9
12	1600	3	3	4	5	5	6	7
13	1800	2	3	3	4	4	5	5
14	2000	2	2	2	3	3	4	4
15	2400	1	1	2	2	2	2	3

Table E8 to Part J Appendix E: Allowable reduction in base thickness for insulated timber frame walls

		Thermal conductivity of insulant (W/mK)
		0.02	0.025	0.03	0.035	0.04	0.045	0.05
	Thermal conductivity of insulation within frame (W/mK)	Reduction in base thickness of insulation for each 100 mm of frame (mm)
	A	B	C	D	E	F	G	H
1	0.035	42	53	63	74	84	95	105
2	0.040	38	48	58	67	77	87	96

Note:

The table is derived for walls for which the proportion of timber is 12%, which corresponds to 48 mm wide studs at 400 mm centres For other proportions of timber the U-value can be calculated using the procedure in Appendix A.

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