Retain Heat Before Adding Heat: Why Loft Insulation Was First

The Advice That Changed Everything

January 2021. New house. 1970s 4-bed detached. The first winter revealed the problem: the house "wasn't great at heating up." I could have bought a bigger boiler. I could have cranked up the thermostat. I could have focused on the heating system first.

Instead, I got some advice that changed my entire approach:

The house had only 50mm of loft insulation—well under current regulations that recommend 270mm+. Heat was escaping through the roof faster than the heating could replace it. Rather than compensating with a bigger, more expensive heating system, I addressed the root cause: the heat loss itself.

The Problem: A House That Wouldn't Hold Heat

Our 1970s house came with original insulation that was decades old and woefully inadequate by modern standards. Only 50mm in the loft when current Building Regulations recommend 270mm minimum. The result was predictable:

• Rooms took forever to warm up
• Landing always cold
• Kitchen freezing in the mornings
• Heat escaping faster than the system could replace it

The Temptation

The obvious solution seemed to be focusing on the heating system:

• Buy a bigger boiler
• Upgrade the radiators
• Crank up the thermostat

All of these would have been treating the symptom, not the cause. I'd be spending money heating the outdoors while the real problem—the house's inability to retain heat—remained unsolved.

Strategic Sequencing

The advice to "retain heat before adding heat" led to a strategic sequence:

• Year 1 (2021): Loft insulation → establish baseline consumption
• Year 2 (2022): Radiators + pipework → enable efficient heat distribution
• Year 3 (2024): Right-sized boiler (826/26kW) → optimized for actual need
• Year 4-5: Optimization (heat curve, weather compensation)

Each step informed by the previous improvements. Better insulation meant lower heat requirements. Lower requirements meant I could right-size the boiler rather than oversize it. A smaller boiler with excellent modulation meant weather compensation could work effectively.

Result: 45.4% total reduction in gas consumption over 5 years, from 18,539 kWh/year to 10,115 kWh/year.

The Economics: £598 vs Other Options

Phase One Cost Breakdown

Total investment: £598.09 inc VAT (January 2021)

• Supplier: Wickes (trade account, 10-15% discount = £56.96 saved)
• Bottom layer: Knauf 100mm insulation (58.1m² coverage)
• Top layer: Knauf 200mm insulation (44.88m² coverage)
• Total added: 300mm (on top of existing 50mm = 350mm total)
• Loft legs: 84 legs (300mm height) for raised flooring
• Flooring: 10 chipboard panels (22mm T&G)
• PPE: Respirator, goggles, boiler suit, gloves = £47
• Electrical: Initial supplies = £29.73

Cost per square meter: approximately £10-13 fully equipped. Professional installation quote estimate: £800-1,200+ for the same area. DIY savings: £200-600+

Compared to Other Efficiency Options

The clear winner: Loft insulation has the lowest cost, shortest payback period, and is DIY-able. It's the smart first step for budget-conscious efficiency improvements.

The ROI Thinking

• £598 investment
• Part of 45.4% total energy reduction over 5 years
• £530/year total savings (all improvements combined)
• Even if loft insulation only contributed 10-15% of savings = £50-80/year
• Payback in 7-12 years, but likely faster
• Plus: increased comfort, reduced drafts, warmer ceilings

The DIY Decision: Why I Did It Myself

My approach to DIY projects follows a simple philosophy:

"If I'm fearful or feel it legally needs someone else, I don't attempt it myself unless the costs of failure are minimal"

Why Loft Insulation Qualified for DIY

• No building regulations notification required (generally)
• No structural changes
• No specialized equipment needed
• Failure costs minimal (worst case: redo some sections)
• Plenty of YouTube tutorials and guides available
• Straightforward process: lay insulation, install loft legs, install boards

The Physical Challenge

The reality: I could not stand up in the corridor or main loft, let alone the edges. The entire project involved working hunched over or crawling. It was physically demanding work in cramped conditions.

The knee pad dilemma: joists were too narrow for comfortable knee padding, making the position even more uncomfortable. This isn't glamorous work—it's hot, cramped, itchy from fiberglass insulation, and physically exhausting.

What I Would Get Professionals For

• Gas work (legally required)
• Major electrical modifications (extending circuits)
• Structural changes (load-bearing walls)
• Anything I'm not confident about
• Anything where failure cost is high

Why DIY made sense here: Cost savings of £200-600+, learn about house construction, satisfaction of doing it yourself, and flexibility to work at your own pace.

The Installation Process: Phase One

Timeline: January-February 2021
Area: Perimeter and end sections
Strategy: Edges and ends first, central boarding later

The Materials

Bottom Layer (100mm):

• Knauf 100mm Space Bottom Layer Loft Roll Insulation
• 7 packs × 8.3m² each = 58.1m² coverage
• Laid between existing joists on top of 50mm existing insulation

Top Layer (200mm):

• Knauf 200mm Super Top Up Loft Roll Insulation
• 8 packs × 5.61m² each = 44.88m² coverage
• Laid perpendicular to bottom layer (cross-hatching prevents thermal bridging)

Total Depth: 300mm added + 50mm existing = 350mm total

• Exceeds current Building Regulations recommendation (270mm)
• Maximum practical depth before diminishing returns

The Loft Leg System

• 84 loft legs (7 packs of 12)
• 300mm height to raise boarding above insulation
• Allows full insulation depth without compression
• Maintains storage space above insulation

The Installation Steps

1. Preparation: Clear loft space, set up lighting, put on full PPE (respirator essential)
2. Initial tidying: Replace some overcrowded junction boxes (this proved insufficient—full electrical overhaul came later in October 2023)
3. Bottom layer: Unroll 100mm insulation between joists, cut to fit around obstacles
4. Top layer: Unroll 200mm insulation perpendicular to bottom layer
5. Loft legs: Position on joists, screw into place for stability
6. Boarding: Lay chipboard panels on loft legs, tongue & groove edges lock together

The Physical Challenge

This was demanding work:

• Cramped conditions throughout—could not stand in most areas
• Hunched over or crawling for entire installation
• Insulation fibers irritate skin despite PPE
• Hot work even in January due to exertion in confined space

Duration: Several weekends (January-February 2021), stopped in February for toilet renovation, resumed Phase 2 in November 2022 when weather cooled.

Why I Stopped: Toilet Renovation & Summer Heat

February 2021: Completed Phase 1 (perimeter and end sections). March-April 2021: Attention turned to downstairs toilet renovation. Practical reality: can't do everything at once.

The Summer Problem

Summer 2021: The loft was too hot to work in for extended periods. Temperatures became unbearable, and physically demanding work in a confined space plus heat equals an unsafe situation. The sensible decision: wait for cooler weather.

The Long Gap

February 2021 → November 2022 = 21 months between phases. Not ideal, but realistic. Life happens: other projects, other priorities. Central boarding could wait—perimeter was done and heat loss already reduced.

The lesson: Phased projects don't need continuous work. Strategic pauses can be smart (seasonal work, other priorities). Don't force work in unsafe conditions. Incremental progress beats abandoned projects.

The Year 1 Baseline: Why This Mattered

Year 1 (post-loft insulation): 18,539 kWh/year consumption. This became the baseline for ALL future improvements. Everything was measured against this number.

Why Baseline Matters

• Can't measure improvement without a starting point
• Year 1 established consumption AFTER insulation
• All future reductions measured from here
• Validates ROI of later improvements

The Total Journey

• Year 1 baseline: 18,539 kWh/year (post-loft)
• Year 5 final: 10,115 kWh/year
• Total reduction: 45.4% (8,424 kWh/year saved)
• Total savings: £530/year vs Year 1

The Compound Effect

Each improvement worked better because of the ones before:

• Better insulation → less heat needed
• Less heat needed → smaller radiators acceptable
• Smaller radiators oversized for low temps → smaller boiler acceptable
• Smaller boiler with good modulation → weather compensation effective
• Weather compensation → heat curve optimization → maximum efficiency

The Electrical Overhaul: October 2023

The initial electrical tidying in January 2021 wasn't enough. Too many cables in junction boxes created an overcrowded "rats nest" and a potential fire risk. Insulation covering them would hamper maintainability and violate building regulations.

The Solution: Hager J804 Maintenance-Free Junction Boxes

The Installation Strategy

• Attached to wooden boards: Mounted on boards spanning between roof webs
• Above insulation level: Clearly visible and accessible for maintenance
• Purpose marked: Each board labeled with circuit purpose ("Landing lights", "Bedroom circuit", etc.)
• Cable management: Over-sleeved older cables with updated colour codes, new cables for power between boxes

The DIY Electrical Work

I did the electrical work myself—not extending circuits (just reorganizing), which I believe is not notifiable work. The systematic process involved:

1. Turn electrics off at consumer unit
2. Go into loft and disconnect one cable
3. Exit loft and go downstairs
4. Turn electrics back on
5. Test which lights no longer work
6. Document the circuit mapping
7. Repeat for each cable

Methodical but time-consuming. Each cable tested individually. Up and down stairs repeatedly. No shortcuts equals safe outcome. No close calls or scary situations—the methodical process avoided mistakes.

The Results: Was It Worth It?

Comfort Improvement

• House holds heat better (noticeable difference)
• Rooms warmer on same thermostat setting
• Ceilings less cold to touch
• Reduced drafts from loft hatch

Energy Consumption

• Year 1 baseline: 18,539 kWh/year (post-loft)
• Contributed to 45.4% total reduction over 5 years
• £530/year total savings (all improvements combined)
• Can't isolate loft insulation alone, but it was the foundation for everything else

The Strategic Payoff

Every subsequent improvement worked better because of loft insulation:

• Radiators didn't need to be as large (heat retained better)
• Boiler didn't need to work as hard
• Lower flow temperatures were practical (house holds heat)
• Weather compensation effective (less heat loss = more control)

ROI Validation

• £598 investment (cheapest efficiency improvement)
• Even if only 10-15% of £530/year savings = £50-80/year
• Payback: 7-12 years from savings alone
• Plus: Comfort improvement (hard to quantify but real)
• Plus: Foundation for optimization (enabled all else)

What Would I Do Differently

Complete the electrical overhaul FIRST (not 2.5 years later). Avoid the initial electrical tidying—it was wasted effort. Go straight to Hager J804 maintenance-free boxes from the start.

Otherwise, the process worked well and the phased approach was sensible.

Would I Do It Again?

Absolutely yes. Best £598 spent on house efficiency. Foundation for everything else. DIY savings significant (£200-600+). Satisfaction of doing it yourself.

Lessons Learned: Advice for Others

1. Start Here First

• Don't upgrade boiler first
• Don't focus on heating system first
• Retain heat before adding heat
• Foundation before optimization

2. The Economic Case

• Lowest cost efficiency improvement (£598 DIY, £800-1,200 professional)
• Shortest payback period (2-4 years typically)
• Enables all other improvements to work better
• No-brainer first step

3. DIY vs Professional

• DIY-able if physically able to work in cramped conditions
• Professional if cramped conditions problematic, time-constrained, or prefer guaranteed work
• DIY savings: £200-600+ but physically demanding
• Either way: Do this first before other efficiency work

4. The Electrical Reality

• Check junction boxes BEFORE insulating
• If overcrowded: Get electrician to relocate FIRST
• Maintenance-free junction boxes above insulation level
• Don't repeat my mistake (initial tidying, then full overhaul 2.5 years later)

5. Phased Approach is Fine

• Don't need to complete all at once
• Perimeter/ends first, central boarding later
• Seasonal work (avoid summer heat)
• Incremental progress beats abandoned projects

6. The PPE Investment

• Proper respirator essential (£23 well spent)
• Goggles prevent fiberglass irritation
• Boiler suit or old clothes you can throw away
• Gloves help but skin will still be itchy
• Don't skimp on PPE

7. The Depth Decision

• 270mm minimum (Building Regs recommendation)
• 300mm+ ideal (diminishing returns beyond 350mm)
• Don't compress insulation (defeats the purpose)
• Cross-hatch layers (prevents thermal bridging)

8. Strategic Timing

• Do this BEFORE other efficiency work
• Establish Year 1 baseline for measuring future improvements
• Cooler months more comfortable to work
• Allow time for phased approach

9. The Mindset

• This isn't glamorous work
• Physically demanding, uncomfortable, itchy
• But: Foundation for everything else
• Best ROI of any efficiency improvement
• Delayed gratification pays off

Conclusion

"Retain heat you're already adding, rather than add more heat."

This advice changed my entire approach to home efficiency. Instead of buying a bigger boiler to compensate for heat loss, I spent £598 insulating the loft properly. From 50mm to 350mm. DIY. Trade account discount.

This wasn't glamorous work. Cramped conditions, fiberglass irritation, physically demanding. But it was the foundation for everything that came after:

• Year 1 baseline: 18,539 kWh/year
• Year 5 final: 10,115 kWh/year
• 45.4% total reduction, £530/year savings

Every subsequent improvement worked better because the loft held heat:

• Oversized radiators practical (heat retained)
• Right-sized boiler practical (lower heat demand)
• Weather compensation effective (predictable heat retention)

The economics: £598 investment (cheapest efficiency improvement), shortest payback period (2-4 years), foundation that enabled £13,149 total investments to work optimally.

Would I do it again? Absolutely. Best £598 spent on the house. Not the most exciting upgrade, but the most important one.

Sometimes the foundation is more important than the finishing touches. This was the foundation.