Target Fixings Limited

There are two basic elements that need to be considered when designing the fixing detail of warm roofs. The wind suction loading is determined by the location of the structure within the UK, the slope of the surrounding land and the structure's overall height. Because of the crushable nature of the insulation material there is an inherent sliding load. The factors that determine the sliding loads are the thickness of the insulation, the slope of the roof and the weight of the roof covering materials. The fixing design will need to address all these factors.

C.P. 3 Chapter V, Part 2, 1972 and amended in 1986, describes a wind exposure chart which is reproduced on the left. Wind Zones A, B and C are defined as follows:  - Wind Zone A - Basic wind speed up to 44 m/s  - Wind Zone B - Basic wind speed of 44 - 52 m/s  - Wind Zone C - Basic wind speed over 52 m/s. The wind suction table, below, takes account of the effects of the slope of the land within 1km. Where the structure height is over 15m the fixing density must be factored by 1.52.

Wind Zone Slope of Land within 1km Suction kN/m² Batten Thickness - mm 25 37 50 A Up to 1:20 2.5 4.0 3.0 2.0 1:20 to 1:12.5 3.5 6.0 3.5 2.5 No Limit 4.7 7.5 5.0 3.5 B Up to 1:20 3.5 6.0 4.0 3.0 1:20 to 1:12.5 4.3 7.0 4.5 3.5 No Limit 6.6 11.0 7.0 5.5 C Up to 1:20 4.1 6.5 4.5 3.0 1:20 to 1:12.5 5.0 8.0 5.5 4.0 No Limit 7.6 12.5 8.5 6.0

Below are the tables we use to calculate the density of Skew Fast that are required to resist sliding loads imposed on the roof. These are calculated using British Standard tables, and take into account the weight of tiles, the pitch of roof, the insulation thickness and whether there is a stop batten installed at the eaves level. The number that is found in the table corresponds to the number of Skew Fast required per square metre to resist sliding loads. Please note that wind loads MUST also be taken into account.

The first three tables below show the impact of using different insulation depths WITH a stop batten installed at eaves level.

Insulation Thickness 36-50mm (WITH STOP BATTEN)
Laid Tile Weight kg/m²	Roof Pitch
	20°	30°	40°	50°	60°	70°	80°	90°
10	3.0	4.0	4.0	3.0	2.0	1.0	1.0	1.0
20	3.5	4.5	4.5	4.0	3.0	2.0	2.0	2.0
30	3.5	5.0	5.0	5.0	4.0	3.0	3.0	3.5
40	4.0	5.5	6.0	5.5	5.0	4.0	4.0	4.5
50	4.5	6.0	6.5	6.5	5.5	5.0	5.0	5.0
60	4.5	6.5	7.0	7.0	6.5	6.0	6.0	6.5
70	5.0	7.0	8.0	8.0	7.5	7.0	7.5	7.5
80	5.5	8.0	8.5	9.0	8.5	8.0	8.5	8.5
90	6.0	8.5	9.5	9.5	9.5	9.0	9.5	9.5
100	7.5	9.0	10.0	10.5	10.5	10.0	10.5	10.5

Insulation Thickness 51-75mm (WITH STOP BATTEN)
Laid Tile Weight kg/m²	Roof Pitch
	20°	30°	40°	50°	60°	70°	80°	90°
10	3.0	4.0	4.0	3.0	2.0	1.0	1.0	1.0
20	3.5	4.5	4.5	4.0	3.0	2.0	2.0	2.0
30	3.5	5.0	5.0	5.0	4.0	3.0	3.0	3.5
40	4.0	5.5	6.0	5.5	5.0	4.0	4.0	4.5
50	4.5	6.0	6.5	6.5	5.5	5.0	5.0	5.0
60	4.5	6.5	7.0	7.0	6.5	6.0	6.0	6.5
70	5.0	7.0	8.0	8.0	7.5	7.0	7.5	7.5
80	5.5	8.0	8.5	9.0	8.5	8.0	8.5	8.5
90	6.0	8.5	9.5	9.5	9.5	9.0	9.5	9.5
100	7.5	9.0	10.0	10.5	10.5	10.0	10.5	10.5

Insulation Thickness 76-150mm (WITH STOP BATTEN)
Laid Tile Weight kg/m²	Roof Pitch
	20°	30°	40°	50°	60°	70°	80°	90°
10	5.5	7.5	7.0	5.5	4.0	2.0	2.0	2.0
20	6.0	8.5	8.0	7.0	5.5	3.5	3.0	3.0
30	6.5	9.0	9.5	8.5	7.0	5.5	5.0	4.0
40	7.5	10.0	10.5	10.0	9.0	7.0	7.0	6.0
50	8.0	11.0	12.0	11.5	10.5	9.0	8.5	8.0
60	8.5	12.0	13.0	13.0	12.0	10.5	10.5	9.5
70	9.0	13.0	14.0	15.0	13.5	11.0	11.0	10.0
80	9.5	14.0	15.0	17.0	15.0	14.0	13.0	11.0
90	10.0	15.0	16.0	18.0	17.0	16.0	14.0	12.0
100	10.5	16.0	17.0	19.0	19.0	17.0	16.0	15.0

The second set of three tables shows the impact of using different insulation depths WITHOUT a stop batten installed at eaves level.

Insulation Thickness 36-50mm (WITHOUT STOP BATTEN)
Laid Tile Weight kg/m²	Roof Pitch
	20°	30°	40°	50°	60°	70°	80°	90°
10	3.0	4.0	4.0	3.0	2.0	1.0	1.0	1.0
20	3.5	4.5	4.5	4.0	3.0	2.0	2.0	2.0
30	3.5	5.0	5.0	5.0	4.0	3.0	3.0	3.5
40	4.0	5.5	6.0	5.5	5.0	4.0	4.0	4.5
50	4.5	6.0	6.5	6.5	5.5	5.0	5.0	5.0
60	4.5	6.5	7.0	7.0	6.5	6.0	6.0	6.5
70	5.0	7.0	8.0	8.0	7.5	7.0	7.5	7.5
80	5.5	8.0	8.5	9.0	8.5	8.0	8.5	8.5
90	6.0	8.5	9.5	9.5	9.5	9.0	9.5	9.5
100	7.5	9.0	10.0	10.5	10.5	10.0	10.5	10.5

Insulation Thickness 51-75mm (WITHOUT STOP BATTEN)
Laid Tile Weight kg/m²	Roof Pitch
	20°	30°	40°	50°	60°	70°	80°	90°
10	5.5	7.5	7.0	5.5	4.0	2.0	2.0	2.0
20	6.0	8.5	8.0	7.0	5.5	3.5	4.0	4.0
30	6.5	9.0	9.5	8.5	7.0	5.5	5.5	6.0
40	7.5	10.0	10.5	10.0	9.0	7.0	7.5	7.5
50	8.0	11.0	12.0	11.5	10.5	9.0	9.5	9.5
60	8.5	12.0	13.0	13.0	12.0	11.0	11.5	11.5
70	9.0	13.0	14.0	15.0	13.5	13.0	13.5	13.5
80	9.5	14.0	15.0	17.0	15.0	15.0	15.5	15.5
90	10.0	15.0	16.0	18.0	17.0	17.0	18.0	18.0
100	10.5	16.0	17.0	19.0	19.0	19.0	20.0	20.0

Insulation Thickness 76-150mm (WITHOUT STOP BATTEN)
Laid Tile Weight kg/m²	Roof Pitch
	20°	30°	40°	50°	60°	70°	80°	90°
10	11.0	15.0	14.0	11.0	8.0	4.0	4.0	4.0
20	12.0	17.0	16.0	14.0	11.0	7.0	8.0	8.0
30	13.0	18.0	19.0	17.0	14.0	11.0	11.0	12.0
40	15.0	20.0	21.0	20.0	18.0	14.0	15.0	15.0
50	16.0	22.0	24.0	22.0	21.0	18.0	19.0	19.0
60	17.0	24.0	26.0	26.0	24.0	22.0	23.0	23.0
70	18.0	26.0	28.0	30.0	27.0	26.0	27.0	27.0
80	19.0	28.0	30.0	34.0	30.0	30.0	31.0	31.5
90	20.0	30.0	32.0	36.0	34.0	34.0	36.0	36.0
100	21.0	32.0	34.0	38.0	38.0	38.0	40.0	40.0

Tile Weights (Laid Weight - Kg/m²)
Marley		Redland
Plain Clay	80	Cambrian Stone	20
Feature	70	Saxon Slate	50
Westwold	100	Richmond Slate	60
Ludlow Plus	50	Stonewall Slate	50
Anglia Plus	50	Delta Slate	60
Double Roman	50	Norfolk Pantile	50
Ludlow Major	50	Regent Tile	50
Mendip	50	Grovebury Double Pantile	50
Modern	50	Bridgewater	50
Wessex	60	50 Double Roman	50
Bold Roll	50	Renown Tile	50
Supalite	30	49 Tile	50
Monarch	20	Downland Plain	50
		Plain Tile	80
		Rosemary Plain Clay	80
		Rosemary Cheslyn Clay	90
Eternit		Anchor Roof Tiles
Rivendale	20	Bold Roll 87	40
Eternit 2000	20	Centurian	30
Duracem	20	Senator	40
Country	20	Vanguard 83	30
Shire	20	Viscount	40
Gower	20	Stone Slate	50
		Anchorlite Slate	30
		Plain Tiles	80
Other		DECRA
Natural Welsh Slate	40	Roofing System	10
Metal Cladding System	10	Stratos	10

General Tile Weights
TILE WEIGHT	Weight Kg/m²
A.C. or Steel Sheet	10
A.C. Slates	20
Natural Slates	30-40
Interlocking Concrete Tiles	40-60
Plain Clay Tiles	60-80
Concrete Slates	90-100
Cotswold Stone	100

The length of the fixing is calculated by the total thickness of material build-up above the rafter plus an additional 35mm for softwood rafters or 25mm for hardwood rafters. Additional length must be allowed for if the rafters have a bow - as is common in barn conversions. The Skew Fast is driven like an ordinary nail, but screws through the counterbatten and into the rafter as it is driven. For lengths over 125mm, a Support Tool should be used, which is a sleeve that goes over the top of the Skew Fast, and - with the Hand Support Tool - hit with a hammer and inserted in the normal way, or - with the Power Support Tool - inserted into an SDS hammer drill on hammer action that can be used to input the fixing. This is to prevent bending of the fixing as it is inserted.

The thickness of the counterbatten will need to be carefully considered. If the thickness of 37mm+ is selected the tile batten may be fixed using an ordinary clout nail. For 25mm to 36mm thickness an improved nail (e.g. 'ring shank') must be used. For counterbattens less than 24mm thick consideration should be given to fixing through the tile batten and counterbatten in one single fixing operation using longer Skew Fast.

The tendency for any sliding load may be decreased by the introduction of a stop batten, usually at eaves level. The stop batten would need to be the same thickness as the insulation material, and is inserted in place of the insulation and is the structurally fixed to the rafters. The counterbattens are then fixed directly on top of the stop-batten. If the roof is long, over 8m, from eaves to ridge, an additional stop-batten should be introduced at the mid-point.

A stop-batten allows the use of much thicker insulation materials with the need for a greatly increased fixing density.