How many Screws do I need?

HOW MANY GROUND SCREWS DO I NEED?

OUR GROUND SCREWS WILL COMFORTABLY ACCOMMODATE THE VAST MAJORITY OF TIMBER FRAMED GARDEN ROOMS OF ALL TYPES. 

FOR DECKING AND TIMBER FRAMED GARDEN ROOM APPLICATIONS PLEASE REFER TO THE FOLLOWING GUIDELINES:

FOR USE WITH 200MM X 50MM (8” X 2”) OR 150MM X 50MM (6” X 2”) BASE JOIST TIMBERS.

FOR 750MM AND 850MM LONG GROUND SCREWS

(Based on a maximum distance of 1700mm between each ground screw).

GROUND SCREW SPACING AND LOAD CHART

JOIST DECK/BASE SIZE
2m
3m
4m
5m
6m
7m
8m
9m
10m
2m - # of screws required
Maximum load - KG
9
9
12
12
15
18
18
21
21
1935
1935
2580
2580
3225
3870
3870
4515
4515
3m - # of screws required
Maximum load - KG
9
9
12
12
15
18
18
21
21
1935
1935
2580
2580
3225
3780
3870
4515
4515
4m - # of screws required
Maximum load - KG
12
12
16
16
20
24
24
28
28
2580
2580
3440
3440
4300
5160
5160
6020
6020
5m - # of screws required
Maximum load - KG
12
12
16
16
20
24
24
28
28
2580
2580
3440
3440
4300
5160
5160
6020
6020
6m - # of screws required
Maximum load - KG
15
15
20
20
25
30
30
35
35
3225
3225
4300
4300
5375
6450
6450
7525
7525
7m - # of screws required
Maximum load - KG
18
18
24
24
30
36
36
42
42
3870
3870
5160
5160
6450
7740
7740
9030
9030
8m - # of screws required
Maximum load - KG
18
18
24
24
30
36
36
42
42
3870
3870
5160
5160
6450
7740
7740
9030
9030
9m - # of screws required
Maximum load - KG
21
21
28
28
35
42
42
49
49
4515
4515
6020
6020
7525
9030
9030
10535
10535
10m - # of screws required
Maximum load - KG
212128283542424949
45154515602060207525903090301053510535

EG: 4 METRES x 7 METRES = 4 ROWS OF 6 = 24 GROUND SCREWS (MAX WEIGHT 5160KG)

ASK YOUR SUPPLIER FOR INFORMATION ON THE WEIGHT OF YOUR BUILDING.

N.B. FOR SMALLER TIMBERS (EG: 4”X 2”) MAXIMUM JOIST SPANS WOULD REDUCE AND THE AMOUNT OF GROUND SCREWS WOULD INCREASE.

 ALWAYS BRACE BETWEEN JOIST SPANS.

THE INFORMATION ABOVE IS BASED ON YOUR WEIGHT BEING REASONABLY EVENLY SPREAD OVER YOUR JOIST BASE.

 EXTRA GROUND SCREWS WOULD BE REQUIRED IF YOU HAVE HEAVY AREAS SUCH AS FOR HOT TUBS ETC, CONTACT US FOR FURTHER INFORMATION.

N.B. THE INFORMATION ABOVE RELATES TO BASE JOISTS THAT ARE SET NO HIGHER THAN 375MM ABOVE GROUND LEVEL,

FOR RAISED PLATFORMS HIGHER THAN 375MM PLEASE CONTACT US FOR FURTHER ADVICE.

 

NOW THE TECHNICAL STUFF! 


ALL LOADING CALCULATIONS BELOW REFER TO 750MM LONG GROUND SCREWS FULLY INSTALLED TO GROUND LEVEL, 

AND TO 850MM LONG GROUND SCREWS INSTALLED TO 175MM ABOVE GROUND LEVEL.

WHEN FULLY INSTALLED IN BEST GROUND CONDITIONS EACH GROUND SCREW CAN WITHSTAND APPROXIMATELY 430KG (0.43 TONNES) OF LOAD.

FOR EXAMPLE:

 IF YOU ARE BUILDING A 5M X 4M BASE USING 6” X 2” JOISTS YOU WOULD REQUIRE 16 GROUND SCREWS.

16 X 430KG = 6880 KG (6.88 TONNE) MAX LOAD

WE WOULD RECOMMEND THIS RESULT IS FACTORED DOWN BY A VALUE OF 50% TO ALLOW FOR ANY POORER GROUND CONDITIONS OR IF THE GROUND SCREWS ARE NOT FULLY INSTALLED TO GROUND LEVEL.

 THEREFORE: WE WOULD RECOMMEND A MAX LOAD OF 3440KG (3.44 TONNES) FOR THE ABOVE EXAMPLE.

THESE CALCULATIONS HAVE BEEN FACTORED INTO THE ‘ SCREW SPACING AND WEIGHT CHART’ ABOVE.

NB: THESE CALCULATIONS CAN BE USED FOR ANY SIZE BASE.


OTHER INFORMATION  

MAXIMUM LOAD: TENSION (PULL OUT) PER GROUND SCREW… 3.10 KN (0.31 TONNES)

MAXIMUM LOAD: HORIZONTAL (SIDEWAYS PRESSURE) PER GROUND SCREW… 1.5 KN (0.15 TONNES)

(The above figures for loading's represent best possible results depending on ground conditions)