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Wall Ties & Restraint Fixings

U-value Calculations

U-value Calculations

Cross-Sectional Areas of Wall Ties for U-value Calculations

For the accurate calculation of U-values for walls it is important to use the correct information for the wall ties.

Using the actual cross-sectional area and the thermal conductivity value of a tie, rather than allowing a program to apply a default value, can make a considerable difference to the calculated U-value. It is widely accepted that default values for wall ties over-estimate the thermal bridging effect.

The actual areas for the main Ancon and Staifix wall ties are shown in the tables below.

The Ancon TeploTie range is manufactured from pultruded basalt fibres set into an epoxy resin. These ties have a thermal conductivity of 0.7W/mk and are the most thermally-efficient wall ties on the market.
Ancon Tie Reference Tie Length (mm) Cavity Width
(mm) 		Wall Tie Type* Area (mm2)
Teplo4 200 50-75 4 12.6
Teplo4 225 76-100 4 12.6
Teplo4 250 101-125 4 12.6
Teplo2 200 50-75 2 19.6
Teplo2 225 76-100 2 19.6
Teplo2 250 101-125 2 19.6
Teplo2 275 126-150 2 28.3
Teplo2 300 151-175 2 28.3
Teplo2 325 176-200 2 28.3
Teplo2 350 201-225 2 38.5
Teplo2 375 226-250 2 38.5
Teplo2 400 251-275 2 38.5
Teplo2 425 276-300 2 38.5
Teplo1 200 50-75 1 38.5
Teplo1 225 76-100 1 38.5
Teplo1 250 101-125 1 38.5
Teplo1 275 126-150 1 38.5

Ancon and Staifix stainless steel wall ties have a thermal conductivity of 17W/mK. They are value-engineered; all unnecessary material is removed to minimise the thermal bridging effect.
Ancon Tie Reference Tie Length
(mm) 		Cavity Width
(mm)
 Wall Tie Type* Area
(mm2)
HRT4 200 50-75 4 3.5
HRT4 225 76-100 4 4.2
HRT4 250 101-125 4 6.2
HRT4 275 126-150 4 6.2
RT2 200 50-75 2 7.5
RT2 225 76-100 2 7.5
RT2 250 101-125 2 8.6
RT2 275 126-150 2 10.2
RT3 200 50-75 3 6.2
RT3 225 76-100 3 6.2
RT3 250 101-125 3 7.5
DT (Double Triangle) 200 50-75 2 7.5
DT (Double Triangle) 225 76-100 2 7.5
DT (Double Triangle) 250 101-125 3 7.5
DT (Double Triangle) 300 150-175 3 8.6
ST1 200 50-75 1 19.5
ST1 225 76-100 1 19.5
ST1 250 101-125 1 19.5
ST1 275 126-150 1 23.4
ST1 300 151-175 1 23.4
TJ2 205-305 50-150 Varies 8.8
STF50 127 50 6 12.0
STF75 152 75 6 12.0
STF100 179 100 6 12.0
TIM6 175-250 50-150 Varies 6.6
SDB/V 125-150 45-94 Varies 38.0
SDB/V 175-200 95-144 Varies 47.5

Masonry-to-masonry wall ties are usually installed at 900mm horizontal centres and 450mm vertical centres; this is equivalent to 2.5 ties/m2. Timber frame are installed at closer centres which is equivalent to a density of 4.4 ties/m2.

Separating (Party) Walls

Ties in separating walls should comply with Approved Document E.

U-value Calculations to BS EN ISO 6946

BS EN ISO 6946 permits the corrections due to wall ties, air gaps etc to be omitted if the corrections amount to less than 3% of the uncorrected U-value of the element.

U-value calculation programs either include a function to allow this 3% rule to be applied (e.g. BRE U-value calculator) or automatically apply it where necessary (e.g. BuildDesk U 3.4).

BuildDesk U 3.4 is available for download as a 30 day free trial by registering here. This program includes Ancon wall ties which can be selected from a drop down menu in preference to the default ties to reduce the U-value calculated. For more information on BuildDesk U visit http://www.builddesk.co.uk/our+software/builddesk+u.

Video File

This BuildDesk U demonstration video entitled 'Changing Wall Ties' highlights how the selection of Ancon wall ties can improve the calculated U-value of a masonry wall.

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