Loft Insulation Thickness Calculator

August 1, 2023 by GEGCalculators

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Loft Insulation Thickness	Recommended R-Value	Recommendation
100mm (4 inches)	R-13	Minimum thickness for basic insulation. Suitable for warmer climates or as additional insulation on top of existing insulation.
150mm (6 inches)	R-19	Standard thickness for moderate climates. Suitable for most homes to achieve decent energy efficiency.
200mm (8 inches)	R-30	Recommended thickness for colder climates. Provides good thermal resistance and energy savings.
270mm (10.5 inches)	R-38	Optimal thickness for colder regions. Offers excellent insulation and energy efficiency.
300mm (12 inches)	R-49	High-performance thickness for extreme cold climates or to meet stringent energy efficiency goals.

Recommendations:

1. Consider your local climate and insulation needs when choosing loft insulation thickness. Colder climates may require thicker insulation for better energy efficiency.
2. For existing homes, check the current insulation thickness and add additional insulation to achieve the recommended R-value.
3. Ensure proper ventilation in the loft space to prevent condensation and maintain airflow.
4. Consider using eco-friendly and non-toxic insulation materials for a safer and healthier living environment.
5. Consult with a professional insulation installer or energy auditor to assess your specific insulation needs and make informed decisions.
6. Regularly inspect and maintain the insulation to ensure its effectiveness and longevity.

Keep in mind that these are general recommendations, and the actual insulation requirements may vary based on factors such as local building codes, climate, and specific insulation materials used. It’s always best to consult with a local expert or insulation professional for personalized advice.

FAQs

1. How thick should my loft insulation be?

The recommended thickness for loft insulation varies depending on the insulation material used and the desired R-value. A typical loft insulation thickness is around 270 mm (approximately 10.5 inches) for mineral wool or fiberglass insulation to achieve the UK’s current recommended R-value of R-38.

2. How do I calculate how much loft insulation I need?

To calculate the amount of loft insulation you need, you’ll need to consider the area of your loft (in square meters or square feet) and the desired R-value. Divide the desired R-value by the thermal resistance per inch of your chosen insulation material to find the required thickness in inches. Then, multiply the thickness by the loft area to get the volume of insulation needed.

3. How thick should insulation be in the attic roof?

The recommended thickness of insulation in the attic roof varies depending on the climate and local building codes. A common recommendation is to have at least 300 mm (approximately 12 inches) of insulation for pitched roofs in colder climates.

4. Can attic insulation be too thick?

While thicker insulation generally provides better thermal performance, there is a limit to how thick attic insulation should be. Overfilling insulation can compress it, reducing its effectiveness and potentially causing other issues. It’s essential to follow manufacturer guidelines and local building codes for insulation thickness.

5. Should loft insulation go right to the edge?

Loft insulation should ideally extend to the edge of the loft or attic space, providing a continuous layer of thermal protection. Insulating right up to the eaves helps prevent cold spots and heat loss around the perimeter of the roof.

6. What R-value should loft insulation have?

The recommended R-value for loft insulation depends on the climate and local regulations. In colder regions, a common recommendation is to have a minimum R-value of R-38 to R-49 for attics.

7. How much air gap for loft insulation?

In most cases, there should not be an air gap between the loft insulation and the roof. Insulation should be installed flush against the roof to prevent heat loss and ensure optimal performance.

8. What is the average loft insulation size?

The average loft insulation size, in terms of thickness, is typically around 270 mm (approximately 10.5 inches). However, the specific size can vary based on the insulation material and desired R-value.

9. What is the best insulation for loft rafters?

For insulating loft rafters, rigid foam board insulation is often used. Polyisocyanurate or extruded polystyrene (XPS) are good choices as they provide high R-values in thinner layers compared to some other insulation types.

10. Is R30 enough for roof insulation?

R-30 insulation is typically considered adequate for roof insulation in moderate climates. However, the specific R-value requirement may vary based on your location and local building codes.

11. How do I know if my attic has enough insulation?

You can check the insulation level in your attic by measuring its thickness with a ruler or tape measure. Alternatively, you can hire a professional to perform an insulation inspection and assess whether your attic has sufficient insulation.

12. Should loft insulation be pushed up to the eaves?

Yes, loft insulation should be installed flush against the roof and pushed up to the eaves to create a continuous thermal barrier and prevent heat loss.

13. Does squashing insulation stop it working?

Squashing or compressing insulation can reduce its effectiveness by decreasing the air pockets within the material, which are responsible for providing thermal resistance. It’s crucial to install insulation properly without compressing it excessively.

14. Should there be a gap in the attic with the insulation?

There should not be an air gap between the insulation and the attic space. The insulation should be installed directly against the ceiling or roof to provide effective thermal protection.

15. Is blown insulation better than rolled?

Blown insulation and rolled insulation both have their advantages. Blown insulation can fill small gaps and irregular spaces better, while rolled insulation is easier to install in standard joist spaces. The choice depends on the specific application and your installer’s expertise.

16. Should you leave a gap between insulation and roof?

No, there should not be a gap between insulation and the roof. The insulation should be installed flush against the roof to provide consistent thermal protection.

17. Where should you not put insulation in the attic?

You should avoid placing insulation directly on top of recessed light fixtures or covering electrical cables and wiring to prevent fire hazards.

18. What are the dos and don’ts of using loft insulation?

Dos:

• Install insulation flush against the roof or ceiling to avoid gaps.
• Ensure proper ventilation to prevent moisture buildup.
• Use appropriate safety gear when handling insulation.

Don’ts:

• Don’t compress insulation excessively.
• Don’t block soffit vents or eave vents.
• Don’t install insulation near heat sources or recessed light fixtures without appropriate clearance.

19. What is the thinnest insulation with the highest R-value?

Aerogel insulation is one of the thinnest insulation materials with an exceptionally high R-value per inch.

20. How long does loft insulation last?

The lifespan of loft insulation depends on the type of material and how well it is maintained. Generally, well-installed insulation can last for several decades.

21. Can I insulate my loft myself?

Yes, many homeowners can install loft insulation themselves, especially with batt or roll-type insulation. However, blown insulation or more complex projects may require professional installation.

22. Can a loft have too much ventilation?

Excessive ventilation in the loft can lead to increased heat loss and energy inefficiency. Proper balance between ventilation and insulation is essential.

23. Does loft insulation need to breathe?

Loft insulation does not need to breathe. It should be installed tightly to provide continuous thermal protection without any air gaps.

24. Can you touch loft insulation?

You can touch loft insulation with caution, but it’s essential to wear appropriate protective gear like gloves, long sleeves, and a dust mask to avoid skin irritation or respiratory issues.

25. Does loft insulation make a big difference?

Yes, loft insulation can make a significant difference in reducing heat loss, lowering energy bills, and improving overall home comfort.

26. How deep is R60 attic insulation?

R60 attic insulation is approximately 457 mm (approximately 18 inches) thick. The thickness may vary depending on the type of insulation used.

27. How many inches of insulation is R38?

R38 insulation is approximately 280 mm (approximately 11 inches) thick.

28. What is recommended loft insulation?

A recommended loft insulation thickness is typically around 270 mm (approximately 10.5 inches) for mineral wool or fiberglass insulation to achieve the UK’s current recommended R-value of R-38.

29. What is the best and safest loft insulation?

Mineral wool and fiberglass insulation are considered safe and widely used in loft insulation projects.

30. What is the cheapest way to insulate loft rafters?

The cheapest way to insulate loft rafters is often using foil-faced rigid foam board insulation, which provides decent R-values at a lower cost compared to other insulation types.

31. Is R19 or R30 better in the attic?

R30 insulation provides higher thermal resistance (R-value) compared to R19, making it better for improving energy efficiency and reducing heat loss.

32. How many inches do you need for R30?

For R30 insulation, you would need approximately 203 mm (approximately 8 inches) of insulation thickness.

33. How many inches is R30 blown insulation?

The thickness of blown insulation required to achieve R30 depends on the specific type of insulation material used and its thermal resistance per inch.

34. What are the signs of poor insulation?

Signs of poor insulation include uneven temperature distribution in the home, high energy bills, drafts, and noticeable hot or cold spots.

35. Does attic insulation go on floor or ceiling?

Attic insulation typically goes on the attic floor, between the ceiling joists, to create a thermal barrier between the living space and the unconditioned attic area.

36. What should insulated attic look like?

An insulated attic should have consistent and evenly distributed insulation between the ceiling joists, covering the entire attic floor.

37. Does insulation go on rafters or the ridge?

Insulation should go on the attic floor, covering the ceiling joists, rather than on the rafters or the ridge.

38. Should attic insulation touch the roof?

No, attic insulation should not touch the roof. It should be installed on the attic floor or between the ceiling joists.

39. Can I lay loft insulation over boards?

You can lay loft insulation over boards, but it’s essential to use loft legs or raised battens to create an air gap to prevent condensation and maintain airflow.

40. What should you not do when installing insulation?

When installing insulation, you should not block soffit vents, cover recessed light fixtures, or compress the insulation excessively.

41. Can I board my loft straight onto joists?

Yes, you can board your loft straight onto joists, but it’s essential to leave an air gap and use insulation beneath the boards to maintain energy efficiency.

42. How tight should insulation be?

Insulation should be installed tightly, without any gaps or spaces, to ensure maximum thermal efficiency.

43. Can you put too much insulation in the attic?

Excessive insulation can lead to diminishing returns, and some insulation materials may become less effective when compressed beyond a certain point.

44. Why don’t you insulate the attic ceiling?

The attic ceiling is typically insulated to create a thermal barrier between the conditioned living space and the unconditioned attic area, preventing heat loss and cold drafts.

45. Can loft insulation be too thick?

Loft insulation can become too thick if it is overfilled or compressed excessively, which can reduce its effectiveness.

46. Should loft insulation go right to the edge?

Yes, loft insulation should extend to the edge of the loft or attic space to provide a continuous layer of thermal protection and prevent heat loss.

47. Can I put new loft insulation on top of old?

In some cases, you can put new loft insulation on top of old insulation to improve overall thermal performance. However, the existing insulation should be in good condition without any signs of damage or deterioration.

48. Can you put 2 layers of insulation in the attic?

Yes, you can install two layers of insulation in the attic to achieve a higher R-value. It’s essential to use different materials or stagger the installation to prevent compression.

49. What is better blown-in cellulose or blown-in fiberglass insulation?

Blown-in cellulose and blown-in fiberglass insulation both have their benefits. Cellulose is more eco-friendly, while fiberglass is non-combustible. The choice depends on specific needs and preferences.

50. What is the best insulation for the attic ceiling?

For the attic ceiling, fiberglass or mineral wool batt insulation is commonly used due to its ease of installation and good thermal performance.

51. Is loose-fill better than batt attic?

Loose-fill and batt insulation both have their advantages. Loose-fill insulation can fill irregular spaces better, while batt insulation is easier to handle and install in standard spaces.

52. Should insulation be above or below rafters?

Insulation is typically installed below the rafters, on the attic floor or between the ceiling joists, to create a thermal barrier between the living space and the unconditioned attic area.

53. Do you need a vapor barrier on both sides of insulation?

In some cases, you may need a vapor barrier on both sides of insulation to prevent moisture from passing through. However, in other situations, a vapor barrier may only be necessary on the warm side of the insulation.

54. Can you over insulate a roof?

Overinsulating a roof can lead to problems such as condensation, ventilation issues, and diminishing returns in terms of energy savings.

55. Is attic insulation more important in winter or summer?

Attic insulation is important throughout the year to maintain a comfortable indoor temperature and reduce energy consumption for both heating in winter and cooling in summer.

56. Should I leave old insulation in attic?

If the old insulation is in good condition and meets the desired R-value, you can leave it in place and add new insulation on top. However, damaged or deteriorated insulation should be replaced.

57. Is it better to insulate ceiling or roof?

It is generally better to insulate the ceiling, creating a thermal barrier between the living space and the unconditioned attic area, rather than insulating the roof itself.

58. Where should you not put insulation in the attic?

You should not put insulation directly on top of recessed light fixtures, cover electrical cables or wiring, or block soffit vents.

59. What not to put in the loft?

In the loft, you should avoid storing items that may be sensitive to temperature fluctuations or prone to damage from potential leaks or condensation.

60. What is the thinnest warmest insulation available?

Aerogel insulation is one of the thinnest and most effective insulation materials available, providing excellent thermal resistance.

61. What is the best R-value per inch?

Aerogel insulation typically offers the highest R-value per inch among commonly available insulation materials.

62. What is the disadvantage of loft insulation?

One potential disadvantage of loft insulation is the risk of condensation if not adequately ventilated. Additionally, improper installation or compression can reduce its effectiveness.

63. How do I know if my loft insulation needs replacing?

You may need to replace loft insulation if it has become damaged, deteriorated, or compressed over time, reducing its thermal performance.

64. Do you need to leave an air gap for insulation?

For some insulation materials and applications, leaving an air gap may be necessary to allow for proper ventilation and prevent condensation. Always follow manufacturer guidelines and local building codes.

65. Does loft insulation need to breathe?

Loft insulation itself does not need to breathe, but it’s essential to ensure adequate ventilation in the loft space to prevent moisture buildup.

66. Should loft insulation be pushed up to the eaves?

Yes, loft insulation should be installed flush against the roof, pushed up to the eaves, to provide a continuous thermal barrier.

67. How can I improve the airflow in my loft?

Improving airflow in the loft can be achieved by providing proper ventilation through soffit vents, ridge vents, or gable vents.

68. What are the dos and don’ts of using loft insulation?

Dos:

• Install insulation flush against the roof or ceiling to avoid gaps.
• Ensure proper ventilation to prevent moisture buildup.
• Use appropriate safety gear when handling insulation.

Don’ts:

• Don’t compress insulation excessively.
• Don’t block soffit vents or eave vents.
• Don’t install insulation near heat sources or recessed light fixtures without appropriate clearance.

69. Can a loft have too much ventilation?

Excessive ventilation in the loft can lead to increased heat loss and energy inefficiency. Proper balance between ventilation and insulation is essential.

70. Does squashing insulation stop it working?

Yes, squashing or compressing insulation can reduce its effectiveness by decreasing the air pockets within the material, which are responsible for providing thermal resistance.

71. How close to edge should loft insulation?

Loft insulation should be installed right up to the edge of the loft or attic space to create a continuous thermal barrier and prevent heat loss.

72. Should you shower after touching insulation?

It is a good practice to shower after touching insulation to wash off any potential irritants and prevent skin irritation.

73. What is the ideal amount of loft insulation?

The ideal amount of loft insulation depends on the insulation material used and the desired R-value. A common recommendation is around 270 mm (approximately 10.5 inches) for mineral wool or fiberglass insulation to achieve R-38.

74. How much warmer can loft insulation make a house?

Properly installed loft insulation can significantly reduce heat loss and make a house noticeably warmer, leading to improved comfort and lower energy bills.

75. Will loft insulation make my house warmer?

Yes, loft insulation can help make your house warmer by reducing heat loss through the roof, improving overall thermal efficiency.

76. Is R60 insulation too much?

R60 insulation is relatively thick and provides high thermal resistance. Whether it is too much depends on your specific climate and energy efficiency goals.

77. How many inches is R49 attic insulation?

R49 attic insulation is approximately 356 mm (approximately 14 inches) thick.

78. How deep is R49 attic insulation?

R49 attic insulation is approximately 356 mm (approximately 14 inches) deep.

79. Which is better R30 or R-38?

R38 insulation provides higher thermal resistance compared to R30, making it better for energy efficiency and reducing heat loss.

80. Which is better R-38 or r49 insulation?

R49 insulation provides higher thermal resistance compared to R38, making it more effective for reducing heat loss and improving energy efficiency.

81. How many inches of spray foam for R-38?

The thickness of spray foam required to achieve R38 depends on the specific type and density of the spray foam used.

82. Can loft insulation be too thick?

Loft insulation can become too thick if it is overfilled or compressed excessively, which can reduce its effectiveness.

83. Is thicker loft insulation better?

Thicker loft insulation generally provides better thermal performance and higher R-value, but there may be practical limitations depending on the available space.

84. What is the best and safest loft insulation?

Mineral wool and fiberglass insulation are considered safe and widely used in loft insulation projects.

85. Should loft insulation be on the roof or floor?

Loft insulation should be installed on the floor, between the ceiling joists, creating a thermal barrier between the living space and the unconditioned attic area.

86. Is it worth putting foil insulation in loft?

Foil insulation can be useful for reflecting radiant heat, but its effectiveness depends on the specific application and other insulation already present.

87. Is new loft insulation better than old?

New loft insulation may offer better thermal performance and higher R-value compared to old insulation, especially if the old insulation is damaged or compressed.

88. Should you insulate between rafters in loft?

Insulating between rafters in the loft can create a conditioned attic space, but it may require additional measures to ensure proper ventilation and prevent moisture issues.

89. Can you lay loft insulation over joists?

You can lay loft insulation over joists, but it’s essential to use loft legs or raised battens to create an air gap to prevent condensation and maintain airflow.

90. Can you stack R19 insulation in attic?

You can stack R19 insulation in the attic to achieve a higher R-value, but ensure the insulation is installed properly and does not compress too much.

91. Can you use R19 for ceiling?

R19 insulation is typically used for walls rather than ceilings. For ceilings, higher R-values are often recommended for better thermal performance.

92. Is R19 worth it over R13?

The choice between R19 and R13 insulation depends on your desired level of insulation and the local climate. R19 provides higher thermal resistance compared to R13.

93. Will R30 fit in 2×8?

R30 insulation typically requires a space of 2×10 to accommodate its thickness.

94. What is the thinnest insulation with the highest R-value?

Aerogel insulation is one of the thinnest and most effective insulation materials available, providing excellent thermal resistance.

95. Is R19 insulation better than R30 insulation?

R30 insulation provides higher thermal resistance compared to R19, making it better for improving energy efficiency and reducing heat loss.

96. Can you have too much attic insulation?

While insulation is essential, having too much attic insulation can lead to problems such as condensation and ventilation issues.

97. How thick should blown attic insulation be?

The recommended thickness of blown attic insulation depends on the desired R-value and the specific insulation material used.

98. Does R30 and R38 make a difference?

R38 provides higher thermal resistance compared to R30, making it more effective for reducing heat loss and improving energy efficiency.

99. What should you not do when installing insulation?

When installing insulation, you should not block soffit vents, cover recessed light fixtures, or compress the insulation excessively.

100. Can too much insulation be bad?

Excessive insulation can lead to diminishing returns, and some insulation materials may become less effective when compressed beyond a certain point.

101. Does insulation get worse over time?

Insulation can deteriorate over time, leading to reduced thermal performance. Proper maintenance and regular inspections are essential to ensure its effectiveness.

102. Where should you not put insulation in the attic?

You should not put insulation directly on top of recessed light fixtures, cover electrical cables or wiring, or block soffit vents.

103. Does loft insulation go over or between joists?

Loft insulation is typically installed between the joists, creating a thermal barrier between the living space and the unconditioned attic area.

104. Should attic insulation be faced up or down?

Attic insulation with a vapor barrier (kraft-faced) should be installed with the facing down toward the heated living space.

105. How do I know if my loft is insulated properly?

You can check the thickness and coverage of insulation in your loft to assess whether it is adequately insulated.

106. How do you know if attic is poorly insulated?

Signs of a poorly insulated attic include uneven temperature distribution, drafts, and high energy bills.

107. Should attic insulation touch the roof?

No, attic insulation should not touch the roof. It should be installed on the attic floor or between the ceiling joists.

108. Is it OK to put insulation between roof rafters?

Insulating between roof rafters can create a conditioned attic space, but it may require additional measures to ensure proper ventilation and prevent moisture issues.

109. How thick should insulation be between rafters?

The thickness of insulation between roof rafters depends on the desired R-value and the specific insulation material used.

110. Should I insulate rafters or joists?

In most cases, insulation is installed between the joists, creating a thermal barrier between the living space and the unconditioned attic area.

111. Does roof insulation need air gap?

Roof insulation typically does not need an air gap, but proper ventilation in the attic is essential to prevent condensation.

112. Which way should insulation face in attic?

For faced insulation with a vapor barrier, the facing should be installed toward the warm side, facing the living space.

113. Do I need insulation baffles in every rafter?

Insulation baffles are not always necessary in every rafter, but they can help ensure proper ventilation and prevent insulation from blocking soffit vents.

114. How much gap do you leave between insulation and loft boards?

It’s essential to leave an air gap between insulation and loft boards to prevent condensation and maintain airflow.

115. Should loft insulation be pushed up to the eaves?

Yes, loft insulation should be installed flush against the roof and pushed up to the eaves to create a continuous thermal barrier.

116. What are the dos and don’ts of using loft insulation?

Dos:

• Install insulation flush against the roof or ceiling to avoid gaps.
• Ensure proper ventilation to prevent moisture buildup.
• Use appropriate safety gear when handling insulation.

Don’ts:

• Don’t compress insulation excessively.
• Don’t block soffit vents or eave vents.
• Don’t install insulation near heat sources or recessed light fixtures without appropriate clearance.

117. Do you put insulation in front or behind wiring?

Insulation should be placed behind wiring to avoid potential fire hazards and allow for proper airflow.

118. Is it bad to double up insulation?

Doubling up insulation can be beneficial for increasing the overall R-value, but it’s crucial to avoid excessive compression and ensure proper ventilation.

119. Can you install insulation wrong?

Yes, improper installation of insulation can lead to reduced effectiveness and potential issues like condensation or ventilation problems.

120. Do you screw or nail loft boards?

Loft boards can be secured with screws or nails, but screws are often preferred as they provide a more secure and stable attachment.

121. How much weight can loft joists take?

The weight that loft joists can support depends on their size and material. Common residential joists can typically handle around 40 pounds per square foot (PSF) of load.

122. How to board a loft cheaply?

To board a loft cheaply, you can consider using chipboard or oriented strand board (OSB) as a cost-effective option.

123. Does squashing insulation stop it working?

Yes, squashing or compressing insulation can reduce its effectiveness by decreasing the air pockets within the material, which are responsible for providing thermal resistance.

124. Should insulation paper be installed in or out?

For faced insulation with a vapor barrier, the facing should be installed toward the warm side, facing the living space.

125. Can loft insulation be too thick?

Loft insulation can become too thick if it is overfilled or compressed excessively, which can reduce its effectiveness.