Knauf Insulation: What I Learned After 7 Years of Specifying Loft Insulation (And a Few $1,000 Mistakes)

I've been ordering insulation materials for commercial and residential projects for about 7 years now. In that time, I've personally made (and documented) around 15 significant specification errors, totaling roughly $8,000 in wasted budget across various jobs. Now I maintain our team's project checklist to prevent repeating those same mistakes.

So when someone asks me about Knauf Insulation — specifically the Eko Roll 200mm for loft insulation, or how it stacks up against Rockwool — I've got opinions. Not theoretical ones. 'I-paid-for-it-and-then-ripped-it-out' kind of opinions.

Here are the questions I get asked most often, answered with the benefit of several thousand dollars of hindsight.

Q1: Is the Knauf Eko Roll 200mm worth it for a loft insulation project?

Short answer: Yes, for most standard loft applications.

The Eko Roll 200mm is basically the workhorse of the Knauf loft range. It's a glass mineral wool roll designed for the space between and over ceiling joists. At 200mm thickness, it hits the current UK Building Regulations target U-value for loft insulation (around 0.16 W/m²K, depending on your setup).

I've used it on about 40+ lofts over the years — both new builds and retrofits. The Ecose technology is a genuine differentiator. It uses a bio-based binder instead of the traditional formaldehyde-based one. The difference you notice immediately? Way less dust and irritation during handling. Honestly, that alone makes it worth considering if your team (or you) are doing the install.

The catch (because there's always one): 200mm is the minimum for current regs in most cases. If you're topping up existing insulation, you might need less. But starting from scratch? Don't go thinner. I learned this the hard way on a project in 2021 where I specified 150mm to save a few quid per roll. It passed inspection, technically, but the homeowner noticed the difference in comfort immediately. Ended up ripping it out and re-doing at 200mm. That mistake cost about $400 in waste plus a week of schedule (ugh).

Q2: Knauf insulation vs Rockwool — which is actually better?

This is the question that starts arguments on building sites. I'm not going to tell you one is universally better, because they're not. But here's what I've found after specifying both.

My take: For a standard loft or wall insulation where budget matters and fire risk is standard (not a high-rise), I usually go Knauf. The cost savings are real, and the Ecose handling difference is a big deal for installation crews. For acoustic separation (party walls, music studios) or where fire is a primary concern (commercial kitchens, high-risk buildings), Rockwool is worth the extra money.

But honestly? For most residential loft insulation, the difference in day-to-day performance isn't as dramatic as the forums make it sound. Both will keep your house warm. The installation quality matters more than the brand.

"Everything I'd read said Rockwool was always the premium choice. In practice, for our standard loft insulation jobs, the mid-tier option (Knauf) actually delivered the same results at a better price."

Q3: What's the biggest mistake people make installing Knauf Eko Roll in a loft?

I've seen three main ones, in order of frequency:

1. Not compressing correctly. Glass mineral wool works by trapping air in tiny pockets. If you squash it down to fit a tighter gap, you reduce those pockets and lower the insulation value. It's counter-intuitive — tighter isn't better. You want it snug but not compressed.
2. Leaving gaps (even small ones). Per US Department of Energy research, gaps as small as 5% of the surface can reduce overall insulation effectiveness by up to 20%. Think about that. A 1-inch gap at every joist can totally undermine your investment.
3. Overlooking the loft hatch. Everyone insulates the floor. Almost everyone forgets the hatch. It's a big uninsulated hole in your thermal envelope. I've seen this on probably 60% of the lofts I've inspected — including my own first project. (Note to self: I really should have checked before the inspection.)

Q4: Is Knauf Ecose technology just marketing hype?

I was skeptical when I first heard about it. Actually, I'll be honest: I thought it was a gimmick. The idea that a mineral wool binder could be 'bio-based' and still perform — sounded like a marketing angle.

But then I did a project where we had to install about 200 square meters of standard glass wool (non-Ecose) in a church hall. Two days of work. Everyone's hands were itching. Dust was everywhere. The client had to air the place out for almost a week.

Next project: a housing development using Knauf Eko Roll. Night and day difference. Less dust, less irritation, easier to cut. The installers actually commented on it. "This stuff doesn't fight back," one of them said.

So is it worth paying a slight premium for? Based on my experience — yes. The handling difference alone translates to faster install, less clean-up, and happier crews. That's not hype, that's time and money saved.

Per FTC Green Guides guidelines (ftc.gov), claims like 'reduced formaldehyde' need substantiation. Knauf has third-party certifications like Eurofins Indoor Air Comfort Gold to back this up. So it's real, not just a label.

Q5: Can I install 200mm loft insulation over existing insulation?

Yes, but with a major caveat: the existing insulation layer needs to be in good condition. No mold, no damp, no rodent damage.

If you're adding 200mm of Knauf Eko Roll on top of, say, 100mm of older fiberglass that's settled and compressed — you're wasting money. The compressed old stuff has lower R-value than its label suggests. You'd be better off removing the old, checking the space for issues, and starting fresh with 200mm of new material.

This is one of those 'I wish I'd known earlier' things. On a project in early 2023, we added new insulation over old in a 1920s house. Looked fine from above. Six months later, the homeowner noticed cold spots. We investigated — old layer was damp in one corner due to a minor roof leak that had been there for years. The new insulation on top just hid the problem until rot set in. Cost us $700 to remediate including fungal treatment. (We cover that now in our pre-check list.)

Q6: What R-value should I aim for with Knauf loft insulation?

This depends on your climate zone, but here's a practical guideline based on Building Regulations Part L (UK) and IECC (US) standards:

• UK Building Regs (Part L): Minimum U-value of 0.16 W/m²K for loft insulation. For glass wool, that typically means 250-270mm total thickness. Though 200mm is on the edge in some situations (especially with thermal bridging through joists).
• US IECC (zone 4-5, like most of the UK): R-38 to R-49 for attics. Glass wool at 200mm is roughly R-6 to R-7 per inch, so 200mm = R-30 to R-33. That's below current recommendations for most US zones. You'd need 250-300mm.

Bottom line: If you're in the UK or similar climate, 200mm Knauf Eko Roll is the minimum you should consider. 250mm is better. Don't try to cut corners on thickness — it's the one spec you really don't want to compromise on.

"The conventional wisdom is to aim for minimum thickness. My experience with 40+ installations suggests that adding 50mm more than the minimum is the most cost-effective upgrade you can make. The material cost is low, the return in comfort and energy savings is disproportionate."

Q7: How do Knauf products compare to Owens Corning or other fiberglass brands?

I won't get into brand wars here (and per company policy, I won't attack competitors directly). But I will give you my honest, experience-based comparison:

• Owens Corning PINK Fiberglas: Similar performance, different binder tech. The PINK stuff uses a different binder system. Both are good. Knauf's Ecose gives it an edge in handling, in my opinion.
• Johns Manville: Comparable quality. JM has a strong formaldehyde-free range too. Price point is similar.
• Rockwool: Already covered. Different material (stone vs glass), different use cases.

The biggest difference I've found is availability and local support. If your local builders' merchant has Knauf in stock consistently and carries the full range with support tools (like the U-value calculator and coverage charts), that's a practical advantage. A product you can get reliably for three years is better than a slightly cheaper one you can't consistently find.

So glad I stopped chasing the 'best' product and started maximizing what's locally available and well-supported. It saves way more than the theoretical performance difference could ever give you.

— Written by a specifier who's made most of these mistakes personally. Currently maintaining our team's insulation project checklist.